eth/downloader: speed up tests by generating chain only once (#17916)

* core: speed up GenerateChain

Use a mock implementation of ChainReader instead of creating
and destroying a BlockChain object for each generated block.

* eth/downloader: speed up tests by generating chain only once

This change reworks the downloader tests so they share a common test
blockchain instead of generating a chain in every test. The tests are
roughly twice as fast now.

2 files changed, 491 insertions, 544 deletions

diff --git a/eth/downloader/downloader_test.go b/eth/downloader/downloader_test.go
index dad626e89..1fe02d884 100644
--- a/eth/downloader/downloader_test.go
+++ b/eth/downloader/downloader_test.go
@@ -25,22 +25,14 @@ import (
 	"testing"
 	"time"
 
+	ethereum "github.com/ethereum/go-ethereum"
 	"github.com/ethereum/go-ethereum/common"
-	"github.com/ethereum/go-ethereum/consensus/ethash"
-	"github.com/ethereum/go-ethereum/core"
 	"github.com/ethereum/go-ethereum/core/types"
-	"github.com/ethereum/go-ethereum/crypto"
 	"github.com/ethereum/go-ethereum/ethdb"
 	"github.com/ethereum/go-ethereum/event"
-	"github.com/ethereum/go-ethereum/params"
 	"github.com/ethereum/go-ethereum/trie"
 )
 
-var (
-	testKey, _  = crypto.HexToECDSA("b71c71a67e1177ad4e901695e1b4b9ee17ae16c6668d313eac2f96dbcda3f291")
-	testAddress = crypto.PubkeyToAddress(testKey.PublicKey)
-)
-
 // Reduce some of the parameters to make the tester faster.
 func init() {
 	MaxForkAncestry = uint64(10000)
@@ -55,6 +47,7 @@ type downloadTester struct {
 	genesis *types.Block   // Genesis blocks used by the tester and peers
 	stateDb ethdb.Database // Database used by the tester for syncing from peers
 	peerDb  ethdb.Database // Database of the peers containing all data
+	peers   map[string]*downloadTesterPeer
 
 	ownHashes   []common.Hash                  // Hash chain belonging to the tester
 	ownHeaders  map[common.Hash]*types.Header  // Headers belonging to the tester
@@ -62,129 +55,27 @@ type downloadTester struct {
 	ownReceipts map[common.Hash]types.Receipts // Receipts belonging to the tester
 	ownChainTd  map[common.Hash]*big.Int       // Total difficulties of the blocks in the local chain
 
-	peerHashes   map[string][]common.Hash                  // Hash chain belonging to different test peers
-	peerHeaders  map[string]map[common.Hash]*types.Header  // Headers belonging to different test peers
-	peerBlocks   map[string]map[common.Hash]*types.Block   // Blocks belonging to different test peers
-	peerReceipts map[string]map[common.Hash]types.Receipts // Receipts belonging to different test peers
-	peerChainTds map[string]map[common.Hash]*big.Int       // Total difficulties of the blocks in the peer chains
-
-	peerMissingStates map[string]map[common.Hash]bool // State entries that fast sync should not return
-
 	lock sync.RWMutex
 }
 
 // newTester creates a new downloader test mocker.
 func newTester() *downloadTester {
-	testdb := ethdb.NewMemDatabase()
-	genesis := core.GenesisBlockForTesting(testdb, testAddress, big.NewInt(1000000000))
-
 	tester := &downloadTester{
-		genesis:           genesis,
-		peerDb:            testdb,
-		ownHashes:         []common.Hash{genesis.Hash()},
-		ownHeaders:        map[common.Hash]*types.Header{genesis.Hash(): genesis.Header()},
-		ownBlocks:         map[common.Hash]*types.Block{genesis.Hash(): genesis},
-		ownReceipts:       map[common.Hash]types.Receipts{genesis.Hash(): nil},
-		ownChainTd:        map[common.Hash]*big.Int{genesis.Hash(): genesis.Difficulty()},
-		peerHashes:        make(map[string][]common.Hash),
-		peerHeaders:       make(map[string]map[common.Hash]*types.Header),
-		peerBlocks:        make(map[string]map[common.Hash]*types.Block),
-		peerReceipts:      make(map[string]map[common.Hash]types.Receipts),
-		peerChainTds:      make(map[string]map[common.Hash]*big.Int),
-		peerMissingStates: make(map[string]map[common.Hash]bool),
+		genesis:     testGenesis,
+		peerDb:      testDB,
+		peers:       make(map[string]*downloadTesterPeer),
+		ownHashes:   []common.Hash{testGenesis.Hash()},
+		ownHeaders:  map[common.Hash]*types.Header{testGenesis.Hash(): testGenesis.Header()},
+		ownBlocks:   map[common.Hash]*types.Block{testGenesis.Hash(): testGenesis},
+		ownReceipts: map[common.Hash]types.Receipts{testGenesis.Hash(): nil},
+		ownChainTd:  map[common.Hash]*big.Int{testGenesis.Hash(): testGenesis.Difficulty()},
 	}
 	tester.stateDb = ethdb.NewMemDatabase()
-	tester.stateDb.Put(genesis.Root().Bytes(), []byte{0x00})
-
+	tester.stateDb.Put(testGenesis.Root().Bytes(), []byte{0x00})
 	tester.downloader = New(FullSync, tester.stateDb, new(event.TypeMux), tester, nil, tester.dropPeer)
-
 	return tester
 }
 
-// makeChain creates a chain of n blocks starting at and including parent.
-// the returned hash chain is ordered head->parent. In addition, every 3rd block
-// contains a transaction and every 5th an uncle to allow testing correct block
-// reassembly.
-func (dl *downloadTester) makeChain(n int, seed byte, parent *types.Block, parentReceipts types.Receipts, heavy bool) ([]common.Hash, map[common.Hash]*types.Header, map[common.Hash]*types.Block, map[common.Hash]types.Receipts) {
-	// Generate the block chain
-	blocks, receipts := core.GenerateChain(params.TestChainConfig, parent, ethash.NewFaker(), dl.peerDb, n, func(i int, block *core.BlockGen) {
-		block.SetCoinbase(common.Address{seed})
-
-		// If a heavy chain is requested, delay blocks to raise difficulty
-		if heavy {
-			block.OffsetTime(-1)
-		}
-		// If the block number is multiple of 3, send a bonus transaction to the miner
-		if parent == dl.genesis && i%3 == 0 {
-			signer := types.MakeSigner(params.TestChainConfig, block.Number())
-			tx, err := types.SignTx(types.NewTransaction(block.TxNonce(testAddress), common.Address{seed}, big.NewInt(1000), params.TxGas, nil, nil), signer, testKey)
-			if err != nil {
-				panic(err)
-			}
-			block.AddTx(tx)
-		}
-		// If the block number is a multiple of 5, add a bonus uncle to the block
-		if i > 0 && i%5 == 0 {
-			block.AddUncle(&types.Header{
-				ParentHash: block.PrevBlock(i - 1).Hash(),
-				Number:     big.NewInt(block.Number().Int64() - 1),
-			})
-		}
-	})
-	// Convert the block-chain into a hash-chain and header/block maps
-	hashes := make([]common.Hash, n+1)
-	hashes[len(hashes)-1] = parent.Hash()
-
-	headerm := make(map[common.Hash]*types.Header, n+1)
-	headerm[parent.Hash()] = parent.Header()
-
-	blockm := make(map[common.Hash]*types.Block, n+1)
-	blockm[parent.Hash()] = parent
-
-	receiptm := make(map[common.Hash]types.Receipts, n+1)
-	receiptm[parent.Hash()] = parentReceipts
-
-	for i, b := range blocks {
-		hashes[len(hashes)-i-2] = b.Hash()
-		headerm[b.Hash()] = b.Header()
-		blockm[b.Hash()] = b
-		receiptm[b.Hash()] = receipts[i]
-	}
-	return hashes, headerm, blockm, receiptm
-}
-
-// makeChainFork creates two chains of length n, such that h1[:f] and
-// h2[:f] are different but have a common suffix of length n-f.
-func (dl *downloadTester) makeChainFork(n, f int, parent *types.Block, parentReceipts types.Receipts, balanced bool) ([]common.Hash, []common.Hash, map[common.Hash]*types.Header, map[common.Hash]*types.Header, map[common.Hash]*types.Block, map[common.Hash]*types.Block, map[common.Hash]types.Receipts, map[common.Hash]types.Receipts) {
-	// Create the common suffix
-	hashes, headers, blocks, receipts := dl.makeChain(n-f, 0, parent, parentReceipts, false)
-
-	// Create the forks, making the second heavier if non balanced forks were requested
-	hashes1, headers1, blocks1, receipts1 := dl.makeChain(f, 1, blocks[hashes[0]], receipts[hashes[0]], false)
-	hashes1 = append(hashes1, hashes[1:]...)
-
-	heavy := false
-	if !balanced {
-		heavy = true
-	}
-	hashes2, headers2, blocks2, receipts2 := dl.makeChain(f, 2, blocks[hashes[0]], receipts[hashes[0]], heavy)
-	hashes2 = append(hashes2, hashes[1:]...)
-
-	for hash, header := range headers {
-		headers1[hash] = header
-		headers2[hash] = header
-	}
-	for hash, block := range blocks {
-		blocks1[hash] = block
-		blocks2[hash] = block
-	}
-	for hash, receipt := range receipts {
-		receipts1[hash] = receipt
-		receipts2[hash] = receipt
-	}
-	return hashes1, hashes2, headers1, headers2, blocks1, blocks2, receipts1, receipts2
-}
-
 // terminate aborts any operations on the embedded downloader and releases all
 // held resources.
 func (dl *downloadTester) terminate() {
@@ -194,13 +85,10 @@ func (dl *downloadTester) terminate() {
 // sync starts synchronizing with a remote peer, blocking until it completes.
 func (dl *downloadTester) sync(id string, td *big.Int, mode SyncMode) error {
 	dl.lock.RLock()
-	hash := dl.peerHashes[id][0]
+	hash := dl.peers[id].chain.headBlock().Hash()
 	// If no particular TD was requested, load from the peer's blockchain
 	if td == nil {
-		td = big.NewInt(1)
-		if diff, ok := dl.peerChainTds[id][hash]; ok {
-			td = diff
-		}
+		td = dl.peers[id].chain.td(hash)
 	}
 	dl.lock.RUnlock()
 
@@ -302,7 +190,7 @@ func (dl *downloadTester) GetTd(hash common.Hash, number uint64) *big.Int {
 }
 
 // InsertHeaderChain injects a new batch of headers into the simulated chain.
-func (dl *downloadTester) InsertHeaderChain(headers []*types.Header, checkFreq int) (int, error) {
+func (dl *downloadTester) InsertHeaderChain(headers []*types.Header, checkFreq int) (i int, err error) {
 	dl.lock.Lock()
 	defer dl.lock.Unlock()
 
@@ -331,7 +219,7 @@ func (dl *downloadTester) InsertHeaderChain(headers []*types.Header, checkFreq i
 }
 
 // InsertChain injects a new batch of blocks into the simulated chain.
-func (dl *downloadTester) InsertChain(blocks types.Blocks) (int, error) {
+func (dl *downloadTester) InsertChain(blocks types.Blocks) (i int, err error) {
 	dl.lock.Lock()
 	defer dl.lock.Unlock()
 
@@ -353,7 +241,7 @@ func (dl *downloadTester) InsertChain(blocks types.Blocks) (int, error) {
 }
 
 // InsertReceiptChain injects a new batch of receipts into the simulated chain.
-func (dl *downloadTester) InsertReceiptChain(blocks types.Blocks, receipts []types.Receipts) (int, error) {
+func (dl *downloadTester) InsertReceiptChain(blocks types.Blocks, receipts []types.Receipts) (i int, err error) {
 	dl.lock.Lock()
 	defer dl.lock.Unlock()
 
@@ -387,60 +275,13 @@ func (dl *downloadTester) Rollback(hashes []common.Hash) {
 }
 
 // newPeer registers a new block download source into the downloader.
-func (dl *downloadTester) newPeer(id string, version int, hashes []common.Hash, headers map[common.Hash]*types.Header, blocks map[common.Hash]*types.Block, receipts map[common.Hash]types.Receipts) error {
-	return dl.newSlowPeer(id, version, hashes, headers, blocks, receipts, 0)
-}
-
-// newSlowPeer registers a new block download source into the downloader, with a
-// specific delay time on processing the network packets sent to it, simulating
-// potentially slow network IO.
-func (dl *downloadTester) newSlowPeer(id string, version int, hashes []common.Hash, headers map[common.Hash]*types.Header, blocks map[common.Hash]*types.Block, receipts map[common.Hash]types.Receipts, delay time.Duration) error {
+func (dl *downloadTester) newPeer(id string, version int, chain *testChain) error {
 	dl.lock.Lock()
 	defer dl.lock.Unlock()
 
-	var err = dl.downloader.RegisterPeer(id, version, &downloadTesterPeer{dl: dl, id: id, delay: delay})
-	if err == nil {
-		// Assign the owned hashes, headers and blocks to the peer (deep copy)
-		dl.peerHashes[id] = make([]common.Hash, len(hashes))
-		copy(dl.peerHashes[id], hashes)
-
-		dl.peerHeaders[id] = make(map[common.Hash]*types.Header)
-		dl.peerBlocks[id] = make(map[common.Hash]*types.Block)
-		dl.peerReceipts[id] = make(map[common.Hash]types.Receipts)
-		dl.peerChainTds[id] = make(map[common.Hash]*big.Int)
-		dl.peerMissingStates[id] = make(map[common.Hash]bool)
-
-		genesis := hashes[len(hashes)-1]
-		if header := headers[genesis]; header != nil {
-			dl.peerHeaders[id][genesis] = header
-			dl.peerChainTds[id][genesis] = header.Difficulty
-		}
-		if block := blocks[genesis]; block != nil {
-			dl.peerBlocks[id][genesis] = block
-			dl.peerChainTds[id][genesis] = block.Difficulty()
-		}
-
-		for i := len(hashes) - 2; i >= 0; i-- {
-			hash := hashes[i]
-
-			if header, ok := headers[hash]; ok {
-				dl.peerHeaders[id][hash] = header
-				if _, ok := dl.peerHeaders[id][header.ParentHash]; ok {
-					dl.peerChainTds[id][hash] = new(big.Int).Add(header.Difficulty, dl.peerChainTds[id][header.ParentHash])
-				}
-			}
-			if block, ok := blocks[hash]; ok {
-				dl.peerBlocks[id][hash] = block
-				if _, ok := dl.peerBlocks[id][block.ParentHash()]; ok {
-					dl.peerChainTds[id][hash] = new(big.Int).Add(block.Difficulty(), dl.peerChainTds[id][block.ParentHash()])
-				}
-			}
-			if receipt, ok := receipts[hash]; ok {
-				dl.peerReceipts[id][hash] = receipt
-			}
-		}
-	}
-	return err
+	peer := &downloadTesterPeer{dl: dl, id: id, chain: chain}
+	dl.peers[id] = peer
+	return dl.downloader.RegisterPeer(id, version, peer)
 }
 
 // dropPeer simulates a hard peer removal from the connection pool.
@@ -448,89 +289,48 @@ func (dl *downloadTester) dropPeer(id string) {
 	dl.lock.Lock()
 	defer dl.lock.Unlock()
 
-	delete(dl.peerHashes, id)
-	delete(dl.peerHeaders, id)
-	delete(dl.peerBlocks, id)
-	delete(dl.peerChainTds, id)
-
+	delete(dl.peers, id)
 	dl.downloader.UnregisterPeer(id)
 }
 
 type downloadTesterPeer struct {
-	dl    *downloadTester
-	id    string
-	delay time.Duration
-	lock  sync.RWMutex
-}
-
-// setDelay is a thread safe setter for the network delay value.
-func (dlp *downloadTesterPeer) setDelay(delay time.Duration) {
-	dlp.lock.Lock()
-	defer dlp.lock.Unlock()
-
-	dlp.delay = delay
-}
-
-// waitDelay is a thread safe way to sleep for the configured time.
-func (dlp *downloadTesterPeer) waitDelay() {
-	dlp.lock.RLock()
-	delay := dlp.delay
-	dlp.lock.RUnlock()
-
-	time.Sleep(delay)
+	dl            *downloadTester
+	id            string
+	lock          sync.RWMutex
+	chain         *testChain
+	missingStates map[common.Hash]bool // State entries that fast sync should not return
 }
 
 // Head constructs a function to retrieve a peer's current head hash
 // and total difficulty.
 func (dlp *downloadTesterPeer) Head() (common.Hash, *big.Int) {
-	dlp.dl.lock.RLock()
-	defer dlp.dl.lock.RUnlock()
-
-	return dlp.dl.peerHashes[dlp.id][0], nil
+	b := dlp.chain.headBlock()
+	return b.Hash(), dlp.chain.td(b.Hash())
 }
 
 // RequestHeadersByHash constructs a GetBlockHeaders function based on a hashed
 // origin; associated with a particular peer in the download tester. The returned
 // function can be used to retrieve batches of headers from the particular peer.
 func (dlp *downloadTesterPeer) RequestHeadersByHash(origin common.Hash, amount int, skip int, reverse bool) error {
-	// Find the canonical number of the hash
-	dlp.dl.lock.RLock()
-	number := uint64(0)
-	for num, hash := range dlp.dl.peerHashes[dlp.id] {
-		if hash == origin {
-			number = uint64(len(dlp.dl.peerHashes[dlp.id]) - num - 1)
-			break
-		}
+	if reverse {
+		panic("reverse header requests not supported")
 	}
-	dlp.dl.lock.RUnlock()
 
-	// Use the absolute header fetcher to satisfy the query
-	return dlp.RequestHeadersByNumber(number, amount, skip, reverse)
+	result := dlp.chain.headersByHash(origin, amount, skip)
+	go dlp.dl.downloader.DeliverHeaders(dlp.id, result)
+	return nil
 }
 
 // RequestHeadersByNumber constructs a GetBlockHeaders function based on a numbered
 // origin; associated with a particular peer in the download tester. The returned
 // function can be used to retrieve batches of headers from the particular peer.
 func (dlp *downloadTesterPeer) RequestHeadersByNumber(origin uint64, amount int, skip int, reverse bool) error {
-	dlp.waitDelay()
-
-	dlp.dl.lock.RLock()
-	defer dlp.dl.lock.RUnlock()
-
-	// Gather the next batch of headers
-	hashes := dlp.dl.peerHashes[dlp.id]
-	headers := dlp.dl.peerHeaders[dlp.id]
-	result := make([]*types.Header, 0, amount)
-	for i := 0; i < amount && len(hashes)-int(origin)-1-i*(skip+1) >= 0; i++ {
-		if header, ok := headers[hashes[len(hashes)-int(origin)-1-i*(skip+1)]]; ok {
-			result = append(result, header)
-		}
+	if reverse {
+		panic("reverse header requests not supported")
 	}
-	// Delay delivery a bit to allow attacks to unfold
-	go func() {
-		time.Sleep(time.Millisecond)
-		dlp.dl.downloader.DeliverHeaders(dlp.id, result)
-	}()
+
+	result := dlp.chain.headersByNumber(origin, amount, skip)
+	go dlp.dl.downloader.DeliverHeaders(dlp.id, result)
 	return nil
 }
 
@@ -538,24 +338,8 @@ func (dlp *downloadTesterPeer) RequestHeadersByNumber(origin uint64, amount int,
 // peer in the download tester. The returned function can be used to retrieve
 // batches of block bodies from the particularly requested peer.
 func (dlp *downloadTesterPeer) RequestBodies(hashes []common.Hash) error {
-	dlp.waitDelay()
-
-	dlp.dl.lock.RLock()
-	defer dlp.dl.lock.RUnlock()
-
-	blocks := dlp.dl.peerBlocks[dlp.id]
-
-	transactions := make([][]*types.Transaction, 0, len(hashes))
-	uncles := make([][]*types.Header, 0, len(hashes))
-
-	for _, hash := range hashes {
-		if block, ok := blocks[hash]; ok {
-			transactions = append(transactions, block.Transactions())
-			uncles = append(uncles, block.Uncles())
-		}
-	}
-	go dlp.dl.downloader.DeliverBodies(dlp.id, transactions, uncles)
-
+	txs, uncles := dlp.chain.bodies(hashes)
+	go dlp.dl.downloader.DeliverBodies(dlp.id, txs, uncles)
 	return nil
 }
 
@@ -563,21 +347,8 @@ func (dlp *downloadTesterPeer) RequestBodies(hashes []common.Hash) error {
 // peer in the download tester. The returned function can be used to retrieve
 // batches of block receipts from the particularly requested peer.
 func (dlp *downloadTesterPeer) RequestReceipts(hashes []common.Hash) error {
-	dlp.waitDelay()
-
-	dlp.dl.lock.RLock()
-	defer dlp.dl.lock.RUnlock()
-
-	receipts := dlp.dl.peerReceipts[dlp.id]
-
-	results := make([][]*types.Receipt, 0, len(hashes))
-	for _, hash := range hashes {
-		if receipt, ok := receipts[hash]; ok {
-			results = append(results, receipt)
-		}
-	}
-	go dlp.dl.downloader.DeliverReceipts(dlp.id, results)
-
+	receipts := dlp.chain.receipts(hashes)
+	go dlp.dl.downloader.DeliverReceipts(dlp.id, receipts)
 	return nil
 }
 
@@ -585,21 +356,18 @@ func (dlp *downloadTesterPeer) RequestReceipts(hashes []common.Hash) error {
 // peer in the download tester. The returned function can be used to retrieve
 // batches of node state data from the particularly requested peer.
 func (dlp *downloadTesterPeer) RequestNodeData(hashes []common.Hash) error {
-	dlp.waitDelay()
-
 	dlp.dl.lock.RLock()
 	defer dlp.dl.lock.RUnlock()
 
 	results := make([][]byte, 0, len(hashes))
 	for _, hash := range hashes {
 		if data, err := dlp.dl.peerDb.Get(hash.Bytes()); err == nil {
-			if !dlp.dl.peerMissingStates[dlp.id][hash] {
+			if !dlp.missingStates[hash] {
 				results = append(results, data)
 			}
 		}
 	}
 	go dlp.dl.downloader.DeliverNodeData(dlp.id, results)
-
 	return nil
 }
 
@@ -639,21 +407,6 @@ func assertOwnForkedChain(t *testing.T, tester *downloadTester, common int, leng
 	if rs := len(tester.ownReceipts); rs != receipts {
 		t.Fatalf("synchronised receipts mismatch: have %v, want %v", rs, receipts)
 	}
-	// Verify the state trie too for fast syncs
-	/*if tester.downloader.mode == FastSync {
-		pivot := uint64(0)
-		var index int
-		if pivot := int(tester.downloader.queue.fastSyncPivot); pivot < common {
-			index = pivot
-		} else {
-			index = len(tester.ownHashes) - lengths[len(lengths)-1] + int(tester.downloader.queue.fastSyncPivot)
-		}
-		if index > 0 {
-			if statedb, err := state.New(tester.ownHeaders[tester.ownHashes[index]].Root, state.NewDatabase(trie.NewDatabase(tester.stateDb))); statedb == nil || err != nil {
-				t.Fatalf("state reconstruction failed: %v", err)
-			}
-		}
-	}*/
 }
 
 // Tests that simple synchronization against a canonical chain works correctly.
@@ -673,16 +426,14 @@ func testCanonicalSynchronisation(t *testing.T, protocol int, mode SyncMode) {
 	defer tester.terminate()
 
 	// Create a small enough block chain to download
-	targetBlocks := blockCacheItems - 15
-	hashes, headers, blocks, receipts := tester.makeChain(targetBlocks, 0, tester.genesis, nil, false)
-
-	tester.newPeer("peer", protocol, hashes, headers, blocks, receipts)
+	chain := testChainBase.shorten(blockCacheItems - 15)
+	tester.newPeer("peer", protocol, chain)
 
 	// Synchronise with the peer and make sure all relevant data was retrieved
 	if err := tester.sync("peer", nil, mode); err != nil {
 		t.Fatalf("failed to synchronise blocks: %v", err)
 	}
-	assertOwnChain(t, tester, targetBlocks+1)
+	assertOwnChain(t, tester, chain.len())
 }
 
 // Tests that if a large batch of blocks are being downloaded, it is throttled
@@ -699,10 +450,8 @@ func testThrottling(t *testing.T, protocol int, mode SyncMode) {
 	defer tester.terminate()
 
 	// Create a long block chain to download and the tester
-	targetBlocks := 8 * blockCacheItems
-	hashes, headers, blocks, receipts := tester.makeChain(targetBlocks, 0, tester.genesis, nil, false)
-
-	tester.newPeer("peer", protocol, hashes, headers, blocks, receipts)
+	targetBlocks := testChainBase.len() - 1
+	tester.newPeer("peer", protocol, testChainBase)
 
 	// Wrap the importer to allow stepping
 	blocked, proceed := uint32(0), make(chan struct{})
@@ -734,9 +483,7 @@ func testThrottling(t *testing.T, protocol int, mode SyncMode) {
 			cached = len(tester.downloader.queue.blockDonePool)
 			if mode == FastSync {
 				if receipts := len(tester.downloader.queue.receiptDonePool); receipts < cached {
-					//if tester.downloader.queue.resultCache[receipts].Header.Number.Uint64() < tester.downloader.queue.fastSyncPivot {
 					cached = receipts
-					//}
 				}
 			}
 			frozen = int(atomic.LoadUint32(&blocked))
@@ -786,24 +533,22 @@ func testForkedSync(t *testing.T, protocol int, mode SyncMode) {
 	tester := newTester()
 	defer tester.terminate()
 
-	// Create a long enough forked chain
-	common, fork := MaxHashFetch, 2*MaxHashFetch
-	hashesA, hashesB, headersA, headersB, blocksA, blocksB, receiptsA, receiptsB := tester.makeChainFork(common+fork, fork, tester.genesis, nil, true)
-
-	tester.newPeer("fork A", protocol, hashesA, headersA, blocksA, receiptsA)
-	tester.newPeer("fork B", protocol, hashesB, headersB, blocksB, receiptsB)
+	chainA := testChainForkLightA.shorten(testChainBase.len() + 80)
+	chainB := testChainForkLightB.shorten(testChainBase.len() + 80)
+	tester.newPeer("fork A", protocol, chainA)
+	tester.newPeer("fork B", protocol, chainB)
 
 	// Synchronise with the peer and make sure all blocks were retrieved
 	if err := tester.sync("fork A", nil, mode); err != nil {
 		t.Fatalf("failed to synchronise blocks: %v", err)
 	}
-	assertOwnChain(t, tester, common+fork+1)
+	assertOwnChain(t, tester, chainA.len())
 
 	// Synchronise with the second peer and make sure that fork is pulled too
 	if err := tester.sync("fork B", nil, mode); err != nil {
 		t.Fatalf("failed to synchronise blocks: %v", err)
 	}
-	assertOwnForkedChain(t, tester, common+1, []int{common + fork + 1, common + fork + 1})
+	assertOwnForkedChain(t, tester, testChainBase.len(), []int{chainA.len(), chainB.len()})
 }
 
 // Tests that synchronising against a much shorter but much heavyer fork works
@@ -821,24 +566,22 @@ func testHeavyForkedSync(t *testing.T, protocol int, mode SyncMode) {
 	tester := newTester()
 	defer tester.terminate()
 
-	// Create a long enough forked chain
-	common, fork := MaxHashFetch, 4*MaxHashFetch
-	hashesA, hashesB, headersA, headersB, blocksA, blocksB, receiptsA, receiptsB := tester.makeChainFork(common+fork, fork, tester.genesis, nil, false)
-
-	tester.newPeer("light", protocol, hashesA, headersA, blocksA, receiptsA)
-	tester.newPeer("heavy", protocol, hashesB[fork/2:], headersB, blocksB, receiptsB)
+	chainA := testChainForkLightA.shorten(testChainBase.len() + 80)
+	chainB := testChainForkHeavy.shorten(testChainBase.len() + 80)
+	tester.newPeer("light", protocol, chainA)
+	tester.newPeer("heavy", protocol, chainB)
 
 	// Synchronise with the peer and make sure all blocks were retrieved
 	if err := tester.sync("light", nil, mode); err != nil {
 		t.Fatalf("failed to synchronise blocks: %v", err)
 	}
-	assertOwnChain(t, tester, common+fork+1)
+	assertOwnChain(t, tester, chainA.len())
 
 	// Synchronise with the second peer and make sure that fork is pulled too
 	if err := tester.sync("heavy", nil, mode); err != nil {
 		t.Fatalf("failed to synchronise blocks: %v", err)
 	}
-	assertOwnForkedChain(t, tester, common+1, []int{common + fork + 1, common + fork/2 + 1})
+	assertOwnForkedChain(t, tester, testChainBase.len(), []int{chainA.len(), chainB.len()})
 }
 
 // Tests that chain forks are contained within a certain interval of the current
@@ -857,18 +600,16 @@ func testBoundedForkedSync(t *testing.T, protocol int, mode SyncMode) {
 	tester := newTester()
 	defer tester.terminate()
 
-	// Create a long enough forked chain
-	common, fork := 13, int(MaxForkAncestry+17)
-	hashesA, hashesB, headersA, headersB, blocksA, blocksB, receiptsA, receiptsB := tester.makeChainFork(common+fork, fork, tester.genesis, nil, true)
-
-	tester.newPeer("original", protocol, hashesA, headersA, blocksA, receiptsA)
-	tester.newPeer("rewriter", protocol, hashesB, headersB, blocksB, receiptsB)
+	chainA := testChainForkLightA
+	chainB := testChainForkLightB
+	tester.newPeer("original", protocol, chainA)
+	tester.newPeer("rewriter", protocol, chainB)
 
 	// Synchronise with the peer and make sure all blocks were retrieved
 	if err := tester.sync("original", nil, mode); err != nil {
 		t.Fatalf("failed to synchronise blocks: %v", err)
 	}
-	assertOwnChain(t, tester, common+fork+1)
+	assertOwnChain(t, tester, chainA.len())
 
 	// Synchronise with the second peer and ensure that the fork is rejected to being too old
 	if err := tester.sync("rewriter", nil, mode); err != errInvalidAncestor {
@@ -893,17 +634,16 @@ func testBoundedHeavyForkedSync(t *testing.T, protocol int, mode SyncMode) {
 	defer tester.terminate()
 
 	// Create a long enough forked chain
-	common, fork := 13, int(MaxForkAncestry+17)
-	hashesA, hashesB, headersA, headersB, blocksA, blocksB, receiptsA, receiptsB := tester.makeChainFork(common+fork, fork, tester.genesis, nil, false)
-
-	tester.newPeer("original", protocol, hashesA, headersA, blocksA, receiptsA)
-	tester.newPeer("heavy-rewriter", protocol, hashesB[MaxForkAncestry-17:], headersB, blocksB, receiptsB) // Root the fork below the ancestor limit
+	chainA := testChainForkLightA
+	chainB := testChainForkHeavy
+	tester.newPeer("original", protocol, chainA)
+	tester.newPeer("heavy-rewriter", protocol, chainB)
 
 	// Synchronise with the peer and make sure all blocks were retrieved
 	if err := tester.sync("original", nil, mode); err != nil {
 		t.Fatalf("failed to synchronise blocks: %v", err)
 	}
-	assertOwnChain(t, tester, common+fork+1)
+	assertOwnChain(t, tester, chainA.len())
 
 	// Synchronise with the second peer and ensure that the fork is rejected to being too old
 	if err := tester.sync("heavy-rewriter", nil, mode); err != errInvalidAncestor {
@@ -924,7 +664,7 @@ func TestInactiveDownloader62(t *testing.T) {
 		t.Errorf("error mismatch: have %v, want %v", err, errNoSyncActive)
 	}
 	if err := tester.downloader.DeliverBodies("bad peer", [][]*types.Transaction{}, [][]*types.Header{}); err != errNoSyncActive {
-		t.Errorf("error mismatch: have %v, want %v", err, errNoSyncActive)
+		t.Errorf("error mismatch: have %v, want  %v", err, errNoSyncActive)
 	}
 }
 
@@ -962,17 +702,8 @@ func testCancel(t *testing.T, protocol int, mode SyncMode) {
 	tester := newTester()
 	defer tester.terminate()
 
-	// Create a small enough block chain to download and the tester
-	targetBlocks := blockCacheItems - 15
-	if targetBlocks >= MaxHashFetch {
-		targetBlocks = MaxHashFetch - 15
-	}
-	if targetBlocks >= MaxHeaderFetch {
-		targetBlocks = MaxHeaderFetch - 15
-	}
-	hashes, headers, blocks, receipts := tester.makeChain(targetBlocks, 0, tester.genesis, nil, false)
-
-	tester.newPeer("peer", protocol, hashes, headers, blocks, receipts)
+	chain := testChainBase.shorten(MaxHeaderFetch)
+	tester.newPeer("peer", protocol, chain)
 
 	// Make sure canceling works with a pristine downloader
 	tester.downloader.Cancel()
@@ -1005,17 +736,16 @@ func testMultiSynchronisation(t *testing.T, protocol int, mode SyncMode) {
 
 	// Create various peers with various parts of the chain
 	targetPeers := 8
-	targetBlocks := targetPeers*blockCacheItems - 15
-	hashes, headers, blocks, receipts := tester.makeChain(targetBlocks, 0, tester.genesis, nil, false)
+	chain := testChainBase.shorten(targetPeers * 100)
 
 	for i := 0; i < targetPeers; i++ {
 		id := fmt.Sprintf("peer #%d", i)
-		tester.newPeer(id, protocol, hashes[i*blockCacheItems:], headers, blocks, receipts)
+		tester.newPeer(id, protocol, chain.shorten(chain.len()/(i+1)))
 	}
 	if err := tester.sync("peer #0", nil, mode); err != nil {
 		t.Fatalf("failed to synchronise blocks: %v", err)
 	}
-	assertOwnChain(t, tester, targetBlocks+1)
+	assertOwnChain(t, tester, chain.len())
 }
 
 // Tests that synchronisations behave well in multi-version protocol environments
@@ -1034,24 +764,23 @@ func testMultiProtoSync(t *testing.T, protocol int, mode SyncMode) {
 	defer tester.terminate()
 
 	// Create a small enough block chain to download
-	targetBlocks := blockCacheItems - 15
-	hashes, headers, blocks, receipts := tester.makeChain(targetBlocks, 0, tester.genesis, nil, false)
+	chain := testChainBase.shorten(blockCacheItems - 15)
 
 	// Create peers of every type
-	tester.newPeer("peer 62", 62, hashes, headers, blocks, nil)
-	tester.newPeer("peer 63", 63, hashes, headers, blocks, receipts)
-	tester.newPeer("peer 64", 64, hashes, headers, blocks, receipts)
+	tester.newPeer("peer 62", 62, chain)
+	tester.newPeer("peer 63", 63, chain)
+	tester.newPeer("peer 64", 64, chain)
 
 	// Synchronise with the requested peer and make sure all blocks were retrieved
 	if err := tester.sync(fmt.Sprintf("peer %d", protocol), nil, mode); err != nil {
 		t.Fatalf("failed to synchronise blocks: %v", err)
 	}
-	assertOwnChain(t, tester, targetBlocks+1)
+	assertOwnChain(t, tester, chain.len())
 
 	// Check that no peers have been dropped off
 	for _, version := range []int{62, 63, 64} {
 		peer := fmt.Sprintf("peer %d", version)
-		if _, ok := tester.peerHashes[peer]; !ok {
+		if _, ok := tester.peers[peer]; !ok {
 			t.Errorf("%s dropped", peer)
 		}
 	}
@@ -1073,10 +802,8 @@ func testEmptyShortCircuit(t *testing.T, protocol int, mode SyncMode) {
 	defer tester.terminate()
 
 	// Create a block chain to download
-	targetBlocks := 2*blockCacheItems - 15
-	hashes, headers, blocks, receipts := tester.makeChain(targetBlocks, 0, tester.genesis, nil, false)
-
-	tester.newPeer("peer", protocol, hashes, headers, blocks, receipts)
+	chain := testChainBase
+	tester.newPeer("peer", protocol, chain)
 
 	// Instrument the downloader to signal body requests
 	bodiesHave, receiptsHave := int32(0), int32(0)
@@ -1090,16 +817,16 @@ func testEmptyShortCircuit(t *testing.T, protocol int, mode SyncMode) {
 	if err := tester.sync("peer", nil, mode); err != nil {
 		t.Fatalf("failed to synchronise blocks: %v", err)
 	}
-	assertOwnChain(t, tester, targetBlocks+1)
+	assertOwnChain(t, tester, chain.len())
 
 	// Validate the number of block bodies that should have been requested
 	bodiesNeeded, receiptsNeeded := 0, 0
-	for _, block := range blocks {
+	for _, block := range chain.blockm {
 		if mode != LightSync && block != tester.genesis && (len(block.Transactions()) > 0 || len(block.Uncles()) > 0) {
 			bodiesNeeded++
 		}
 	}
-	for _, receipt := range receipts {
+	for _, receipt := range chain.receiptm {
 		if mode == FastSync && len(receipt) > 0 {
 			receiptsNeeded++
 		}
@@ -1127,24 +854,20 @@ func testMissingHeaderAttack(t *testing.T, protocol int, mode SyncMode) {
 	tester := newTester()
 	defer tester.terminate()
 
-	// Create a small enough block chain to download
-	targetBlocks := blockCacheItems - 15
-	hashes, headers, blocks, receipts := tester.makeChain(targetBlocks, 0, tester.genesis, nil, false)
-
-	// Attempt a full sync with an attacker feeding gapped headers
-	tester.newPeer("attack", protocol, hashes, headers, blocks, receipts)
-	missing := targetBlocks / 2
-	delete(tester.peerHeaders["attack"], hashes[missing])
+	chain := testChainBase.shorten(blockCacheItems - 15)
+	brokenChain := chain.shorten(chain.len())
+	delete(brokenChain.headerm, brokenChain.chain[brokenChain.len()/2])
+	tester.newPeer("attack", protocol, brokenChain)
 
 	if err := tester.sync("attack", nil, mode); err == nil {
 		t.Fatalf("succeeded attacker synchronisation")
 	}
 	// Synchronise with the valid peer and make sure sync succeeds
-	tester.newPeer("valid", protocol, hashes, headers, blocks, receipts)
+	tester.newPeer("valid", protocol, chain)
 	if err := tester.sync("valid", nil, mode); err != nil {
 		t.Fatalf("failed to synchronise blocks: %v", err)
 	}
-	assertOwnChain(t, tester, targetBlocks+1)
+	assertOwnChain(t, tester, chain.len())
 }
 
 // Tests that if requested headers are shifted (i.e. first is missing), the queue
@@ -1162,25 +885,24 @@ func testShiftedHeaderAttack(t *testing.T, protocol int, mode SyncMode) {
 	tester := newTester()
 	defer tester.terminate()
 
-	// Create a small enough block chain to download
-	targetBlocks := blockCacheItems - 15
-	hashes, headers, blocks, receipts := tester.makeChain(targetBlocks, 0, tester.genesis, nil, false)
+	chain := testChainBase.shorten(blockCacheItems - 15)
 
 	// Attempt a full sync with an attacker feeding shifted headers
-	tester.newPeer("attack", protocol, hashes, headers, blocks, receipts)
-	delete(tester.peerHeaders["attack"], hashes[len(hashes)-2])
-	delete(tester.peerBlocks["attack"], hashes[len(hashes)-2])
-	delete(tester.peerReceipts["attack"], hashes[len(hashes)-2])
-
+	brokenChain := chain.shorten(chain.len())
+	delete(brokenChain.headerm, brokenChain.chain[1])
+	delete(brokenChain.blockm, brokenChain.chain[1])
+	delete(brokenChain.receiptm, brokenChain.chain[1])
+	tester.newPeer("attack", protocol, brokenChain)
 	if err := tester.sync("attack", nil, mode); err == nil {
 		t.Fatalf("succeeded attacker synchronisation")
 	}
+
 	// Synchronise with the valid peer and make sure sync succeeds
-	tester.newPeer("valid", protocol, hashes, headers, blocks, receipts)
+	tester.newPeer("valid", protocol, chain)
 	if err := tester.sync("valid", nil, mode); err != nil {
 		t.Fatalf("failed to synchronise blocks: %v", err)
 	}
-	assertOwnChain(t, tester, targetBlocks+1)
+	assertOwnChain(t, tester, chain.len())
 }
 
 // Tests that upon detecting an invalid header, the recent ones are rolled back
@@ -1198,13 +920,14 @@ func testInvalidHeaderRollback(t *testing.T, protocol int, mode SyncMode) {
 
 	// Create a small enough block chain to download
 	targetBlocks := 3*fsHeaderSafetyNet + 256 + fsMinFullBlocks
-	hashes, headers, blocks, receipts := tester.makeChain(targetBlocks, 0, tester.genesis, nil, false)
+	chain := testChainBase.shorten(targetBlocks)
 
 	// Attempt to sync with an attacker that feeds junk during the fast sync phase.
 	// This should result in the last fsHeaderSafetyNet headers being rolled back.
-	tester.newPeer("fast-attack", protocol, hashes, headers, blocks, receipts)
 	missing := fsHeaderSafetyNet + MaxHeaderFetch + 1
-	delete(tester.peerHeaders["fast-attack"], hashes[len(hashes)-missing])
+	fastAttackChain := chain.shorten(chain.len())
+	delete(fastAttackChain.headerm, fastAttackChain.chain[missing])
+	tester.newPeer("fast-attack", protocol, fastAttackChain)
 
 	if err := tester.sync("fast-attack", nil, mode); err == nil {
 		t.Fatalf("succeeded fast attacker synchronisation")
@@ -1212,13 +935,15 @@ func testInvalidHeaderRollback(t *testing.T, protocol int, mode SyncMode) {
 	if head := tester.CurrentHeader().Number.Int64(); int(head) > MaxHeaderFetch {
 		t.Errorf("rollback head mismatch: have %v, want at most %v", head, MaxHeaderFetch)
 	}
+
 	// Attempt to sync with an attacker that feeds junk during the block import phase.
 	// This should result in both the last fsHeaderSafetyNet number of headers being
 	// rolled back, and also the pivot point being reverted to a non-block status.
-	tester.newPeer("block-attack", protocol, hashes, headers, blocks, receipts)
 	missing = 3*fsHeaderSafetyNet + MaxHeaderFetch + 1
-	delete(tester.peerHeaders["fast-attack"], hashes[len(hashes)-missing]) // Make sure the fast-attacker doesn't fill in
-	delete(tester.peerHeaders["block-attack"], hashes[len(hashes)-missing])
+	blockAttackChain := chain.shorten(chain.len())
+	delete(fastAttackChain.headerm, fastAttackChain.chain[missing]) // Make sure the fast-attacker doesn't fill in
+	delete(blockAttackChain.headerm, blockAttackChain.chain[missing])
+	tester.newPeer("block-attack", protocol, blockAttackChain)
 
 	if err := tester.sync("block-attack", nil, mode); err == nil {
 		t.Fatalf("succeeded block attacker synchronisation")
@@ -1231,19 +956,18 @@ func testInvalidHeaderRollback(t *testing.T, protocol int, mode SyncMode) {
 			t.Errorf("fast sync pivot block #%d not rolled back", head)
 		}
 	}
+
 	// Attempt to sync with an attacker that withholds promised blocks after the
 	// fast sync pivot point. This could be a trial to leave the node with a bad
 	// but already imported pivot block.
-	tester.newPeer("withhold-attack", protocol, hashes, headers, blocks, receipts)
-	missing = 3*fsHeaderSafetyNet + MaxHeaderFetch + 1
-
+	withholdAttackChain := chain.shorten(chain.len())
+	tester.newPeer("withhold-attack", protocol, withholdAttackChain)
 	tester.downloader.syncInitHook = func(uint64, uint64) {
-		for i := missing; i <= len(hashes); i++ {
-			delete(tester.peerHeaders["withhold-attack"], hashes[len(hashes)-i])
+		for i := missing; i < withholdAttackChain.len(); i++ {
+			delete(withholdAttackChain.headerm, withholdAttackChain.chain[i])
 		}
 		tester.downloader.syncInitHook = nil
 	}
-
 	if err := tester.sync("withhold-attack", nil, mode); err == nil {
 		t.Fatalf("succeeded withholding attacker synchronisation")
 	}
@@ -1255,20 +979,21 @@ func testInvalidHeaderRollback(t *testing.T, protocol int, mode SyncMode) {
 			t.Errorf("fast sync pivot block #%d not rolled back", head)
 		}
 	}
-	// Synchronise with the valid peer and make sure sync succeeds. Since the last
-	// rollback should also disable fast syncing for this process, verify that we
-	// did a fresh full sync. Note, we can't assert anything about the receipts
-	// since we won't purge the database of them, hence we can't use assertOwnChain.
-	tester.newPeer("valid", protocol, hashes, headers, blocks, receipts)
+
+	// synchronise with the valid peer and make sure sync succeeds. Since the last rollback
+	// should also disable fast syncing for this process, verify that we did a fresh full
+	// sync. Note, we can't assert anything about the receipts since we won't purge the
+	// database of them, hence we can't use assertOwnChain.
+	tester.newPeer("valid", protocol, chain)
 	if err := tester.sync("valid", nil, mode); err != nil {
 		t.Fatalf("failed to synchronise blocks: %v", err)
 	}
-	if hs := len(tester.ownHeaders); hs != len(headers) {
-		t.Fatalf("synchronised headers mismatch: have %v, want %v", hs, len(headers))
+	if hs := len(tester.ownHeaders); hs != chain.len() {
+		t.Fatalf("synchronised headers mismatch: have %v, want %v", hs, chain.len())
 	}
 	if mode != LightSync {
-		if bs := len(tester.ownBlocks); bs != len(blocks) {
-			t.Fatalf("synchronised blocks mismatch: have %v, want %v", bs, len(blocks))
+		if bs := len(tester.ownBlocks); bs != chain.len() {
+			t.Fatalf("synchronised blocks mismatch: have %v, want %v", bs, chain.len())
 		}
 	}
 }
@@ -1288,9 +1013,8 @@ func testHighTDStarvationAttack(t *testing.T, protocol int, mode SyncMode) {
 	tester := newTester()
 	defer tester.terminate()
 
-	hashes, headers, blocks, receipts := tester.makeChain(0, 0, tester.genesis, nil, false)
-	tester.newPeer("attack", protocol, []common.Hash{hashes[0]}, headers, blocks, receipts)
-
+	chain := testChainBase.shorten(1)
+	tester.newPeer("attack", protocol, chain)
 	if err := tester.sync("attack", big.NewInt(1000000), mode); err != errStallingPeer {
 		t.Fatalf("synchronisation error mismatch: have %v, want %v", err, errStallingPeer)
 	}
@@ -1333,21 +1057,22 @@ func testBlockHeaderAttackerDropping(t *testing.T, protocol int) {
 	// Run the tests and check disconnection status
 	tester := newTester()
 	defer tester.terminate()
+	chain := testChainBase.shorten(1)
 
 	for i, tt := range tests {
 		// Register a new peer and ensure it's presence
 		id := fmt.Sprintf("test %d", i)
-		if err := tester.newPeer(id, protocol, []common.Hash{tester.genesis.Hash()}, nil, nil, nil); err != nil {
+		if err := tester.newPeer(id, protocol, chain); err != nil {
 			t.Fatalf("test %d: failed to register new peer: %v", i, err)
 		}
-		if _, ok := tester.peerHashes[id]; !ok {
+		if _, ok := tester.peers[id]; !ok {
 			t.Fatalf("test %d: registered peer not found", i)
 		}
 		// Simulate a synchronisation and check the required result
 		tester.downloader.synchroniseMock = func(string, common.Hash) error { return tt.result }
 
 		tester.downloader.Synchronise(id, tester.genesis.Hash(), big.NewInt(1000), FullSync)
-		if _, ok := tester.peerHashes[id]; !ok != tt.drop {
+		if _, ok := tester.peers[id]; !ok != tt.drop {
 			t.Errorf("test %d: peer drop mismatch for %v: have %v, want %v", i, tt.result, !ok, tt.drop)
 		}
 	}
@@ -1367,10 +1092,7 @@ func testSyncProgress(t *testing.T, protocol int, mode SyncMode) {
 
 	tester := newTester()
 	defer tester.terminate()
-
-	// Create a small enough block chain to download
-	targetBlocks := blockCacheItems - 15
-	hashes, headers, blocks, receipts := tester.makeChain(targetBlocks, 0, tester.genesis, nil, false)
+	chain := testChainBase.shorten(blockCacheItems - 15)
 
 	// Set a sync init hook to catch progress changes
 	starting := make(chan struct{})
@@ -1380,12 +1102,10 @@ func testSyncProgress(t *testing.T, protocol int, mode SyncMode) {
 		starting <- struct{}{}
 		<-progress
 	}
-	// Retrieve the sync progress and ensure they are zero (pristine sync)
-	if progress := tester.downloader.Progress(); progress.StartingBlock != 0 || progress.CurrentBlock != 0 || progress.HighestBlock != 0 {
-		t.Fatalf("Pristine progress mismatch: have %v/%v/%v, want %v/%v/%v", progress.StartingBlock, progress.CurrentBlock, progress.HighestBlock, 0, 0, 0)
-	}
+	checkProgress(t, tester.downloader, "pristine", ethereum.SyncProgress{})
+
 	// Synchronise half the blocks and check initial progress
-	tester.newPeer("peer-half", protocol, hashes[targetBlocks/2:], headers, blocks, receipts)
+	tester.newPeer("peer-half", protocol, chain.shorten(chain.len()/2))
 	pending := new(sync.WaitGroup)
 	pending.Add(1)
 
@@ -1396,16 +1116,15 @@ func testSyncProgress(t *testing.T, protocol int, mode SyncMode) {
 		}
 	}()
 	<-starting
-	if progress := tester.downloader.Progress(); progress.StartingBlock != 0 || progress.CurrentBlock != 0 || progress.HighestBlock != uint64(targetBlocks/2+1) {
-		t.Fatalf("Initial progress mismatch: have %v/%v/%v, want %v/%v/%v", progress.StartingBlock, progress.CurrentBlock, progress.HighestBlock, 0, 0, targetBlocks/2+1)
-	}
+	checkProgress(t, tester.downloader, "initial", ethereum.SyncProgress{
+		HighestBlock: uint64(chain.len()/2 - 1),
+	})
 	progress <- struct{}{}
 	pending.Wait()
 
 	// Synchronise all the blocks and check continuation progress
-	tester.newPeer("peer-full", protocol, hashes, headers, blocks, receipts)
+	tester.newPeer("peer-full", protocol, chain)
 	pending.Add(1)
-
 	go func() {
 		defer pending.Done()
 		if err := tester.sync("peer-full", nil, mode); err != nil {
@@ -1413,15 +1132,29 @@ func testSyncProgress(t *testing.T, protocol int, mode SyncMode) {
 		}
 	}()
 	<-starting
-	if progress := tester.downloader.Progress(); progress.StartingBlock != uint64(targetBlocks/2+1) || progress.CurrentBlock != uint64(targetBlocks/2+1) || progress.HighestBlock != uint64(targetBlocks) {
-		t.Fatalf("Completing progress mismatch: have %v/%v/%v, want %v/%v/%v", progress.StartingBlock, progress.CurrentBlock, progress.HighestBlock, targetBlocks/2+1, targetBlocks/2+1, targetBlocks)
-	}
+	checkProgress(t, tester.downloader, "completing", ethereum.SyncProgress{
+		StartingBlock: uint64(chain.len()/2 - 1),
+		CurrentBlock:  uint64(chain.len()/2 - 1),
+		HighestBlock:  uint64(chain.len() - 1),
+	})
+
+	// Check final progress after successful sync
 	progress <- struct{}{}
 	pending.Wait()
+	checkProgress(t, tester.downloader, "final", ethereum.SyncProgress{
+		StartingBlock: uint64(chain.len()/2 - 1),
+		CurrentBlock:  uint64(chain.len() - 1),
+		HighestBlock:  uint64(chain.len() - 1),
+	})
+}
 
-	// Check final progress after successful sync
-	if progress := tester.downloader.Progress(); progress.StartingBlock != uint64(targetBlocks/2+1) || progress.CurrentBlock != uint64(targetBlocks) || progress.HighestBlock != uint64(targetBlocks) {
-		t.Fatalf("Final progress mismatch: have %v/%v/%v, want %v/%v/%v", progress.StartingBlock, progress.CurrentBlock, progress.HighestBlock, targetBlocks/2+1, targetBlocks, targetBlocks)
+func checkProgress(t *testing.T, d *Downloader, stage string, want ethereum.SyncProgress) {
+	t.Helper()
+	p := d.Progress()
+	p.KnownStates, p.PulledStates = 0, 0
+	want.KnownStates, want.PulledStates = 0, 0
+	if p != want {
+		t.Fatalf("%s progress mismatch:\nhave %+v\nwant %+v", stage, p, want)
 	}
 }
 
@@ -1440,10 +1173,8 @@ func testForkedSyncProgress(t *testing.T, protocol int, mode SyncMode) {
 
 	tester := newTester()
 	defer tester.terminate()
-
-	// Create a forked chain to simulate origin revertal
-	common, fork := MaxHashFetch, 2*MaxHashFetch
-	hashesA, hashesB, headersA, headersB, blocksA, blocksB, receiptsA, receiptsB := tester.makeChainFork(common+fork, fork, tester.genesis, nil, true)
+	chainA := testChainForkLightA.shorten(testChainBase.len() + MaxHashFetch)
+	chainB := testChainForkLightB.shorten(testChainBase.len() + MaxHashFetch)
 
 	// Set a sync init hook to catch progress changes
 	starting := make(chan struct{})
@@ -1453,15 +1184,12 @@ func testForkedSyncProgress(t *testing.T, protocol int, mode SyncMode) {
 		starting <- struct{}{}
 		<-progress
 	}
-	// Retrieve the sync progress and ensure they are zero (pristine sync)
-	if progress := tester.downloader.Progress(); progress.StartingBlock != 0 || progress.CurrentBlock != 0 || progress.HighestBlock != 0 {
-		t.Fatalf("Pristine progress mismatch: have %v/%v/%v, want %v/%v/%v", progress.StartingBlock, progress.CurrentBlock, progress.HighestBlock, 0, 0, 0)
-	}
+	checkProgress(t, tester.downloader, "pristine", ethereum.SyncProgress{})
+
 	// Synchronise with one of the forks and check progress
-	tester.newPeer("fork A", protocol, hashesA, headersA, blocksA, receiptsA)
+	tester.newPeer("fork A", protocol, chainA)
 	pending := new(sync.WaitGroup)
 	pending.Add(1)
-
 	go func() {
 		defer pending.Done()
 		if err := tester.sync("fork A", nil, mode); err != nil {
@@ -1469,9 +1197,10 @@ func testForkedSyncProgress(t *testing.T, protocol int, mode SyncMode) {
 		}
 	}()
 	<-starting
-	if progress := tester.downloader.Progress(); progress.StartingBlock != 0 || progress.CurrentBlock != 0 || progress.HighestBlock != uint64(len(hashesA)-1) {
-		t.Fatalf("Initial progress mismatch: have %v/%v/%v, want %v/%v/%v", progress.StartingBlock, progress.CurrentBlock, progress.HighestBlock, 0, 0, len(hashesA)-1)
-	}
+
+	checkProgress(t, tester.downloader, "initial", ethereum.SyncProgress{
+		HighestBlock: uint64(chainA.len() - 1),
+	})
 	progress <- struct{}{}
 	pending.Wait()
 
@@ -1479,9 +1208,8 @@ func testForkedSyncProgress(t *testing.T, protocol int, mode SyncMode) {
 	tester.downloader.syncStatsChainOrigin = tester.downloader.syncStatsChainHeight
 
 	// Synchronise with the second fork and check progress resets
-	tester.newPeer("fork B", protocol, hashesB, headersB, blocksB, receiptsB)
+	tester.newPeer("fork B", protocol, chainB)
 	pending.Add(1)
-
 	go func() {
 		defer pending.Done()
 		if err := tester.sync("fork B", nil, mode); err != nil {
@@ -1489,16 +1217,20 @@ func testForkedSyncProgress(t *testing.T, protocol int, mode SyncMode) {
 		}
 	}()
 	<-starting
-	if progress := tester.downloader.Progress(); progress.StartingBlock != uint64(common) || progress.CurrentBlock != uint64(len(hashesA)-1) || progress.HighestBlock != uint64(len(hashesB)-1) {
-		t.Fatalf("Forking progress mismatch: have %v/%v/%v, want %v/%v/%v", progress.StartingBlock, progress.CurrentBlock, progress.HighestBlock, common, len(hashesA)-1, len(hashesB)-1)
-	}
-	progress <- struct{}{}
-	pending.Wait()
+	checkProgress(t, tester.downloader, "forking", ethereum.SyncProgress{
+		StartingBlock: uint64(testChainBase.len()) - 1,
+		CurrentBlock:  uint64(chainA.len() - 1),
+		HighestBlock:  uint64(chainB.len() - 1),
+	})
 
 	// Check final progress after successful sync
-	if progress := tester.downloader.Progress(); progress.StartingBlock != uint64(common) || progress.CurrentBlock != uint64(len(hashesB)-1) || progress.HighestBlock != uint64(len(hashesB)-1) {
-		t.Fatalf("Final progress mismatch: have %v/%v/%v, want %v/%v/%v", progress.StartingBlock, progress.CurrentBlock, progress.HighestBlock, common, len(hashesB)-1, len(hashesB)-1)
-	}
+	progress <- struct{}{}
+	pending.Wait()
+	checkProgress(t, tester.downloader, "final", ethereum.SyncProgress{
+		StartingBlock: uint64(testChainBase.len()) - 1,
+		CurrentBlock:  uint64(chainB.len() - 1),
+		HighestBlock:  uint64(chainB.len() - 1),
+	})
 }
 
 // Tests that if synchronisation is aborted due to some failure, then the progress
@@ -1516,10 +1248,7 @@ func testFailedSyncProgress(t *testing.T, protocol int, mode SyncMode) {
 
 	tester := newTester()
 	defer tester.terminate()
-
-	// Create a small enough block chain to download
-	targetBlocks := blockCacheItems - 15
-	hashes, headers, blocks, receipts := tester.makeChain(targetBlocks, 0, tester.genesis, nil, false)
+	chain := testChainBase.shorten(blockCacheItems - 15)
 
 	// Set a sync init hook to catch progress changes
 	starting := make(chan struct{})
@@ -1529,20 +1258,18 @@ func testFailedSyncProgress(t *testing.T, protocol int, mode SyncMode) {
 		starting <- struct{}{}
 		<-progress
 	}
-	// Retrieve the sync progress and ensure they are zero (pristine sync)
-	if progress := tester.downloader.Progress(); progress.StartingBlock != 0 || progress.CurrentBlock != 0 || progress.HighestBlock != 0 {
-		t.Fatalf("Pristine progress mismatch: have %v/%v/%v, want %v/%v/%v", progress.StartingBlock, progress.CurrentBlock, progress.HighestBlock, 0, 0, 0)
-	}
+	checkProgress(t, tester.downloader, "pristine", ethereum.SyncProgress{})
+
 	// Attempt a full sync with a faulty peer
-	tester.newPeer("faulty", protocol, hashes, headers, blocks, receipts)
-	missing := targetBlocks / 2
-	delete(tester.peerHeaders["faulty"], hashes[missing])
-	delete(tester.peerBlocks["faulty"], hashes[missing])
-	delete(tester.peerReceipts["faulty"], hashes[missing])
+	brokenChain := chain.shorten(chain.len())
+	missing := brokenChain.len() / 2
+	delete(brokenChain.headerm, brokenChain.chain[missing])
+	delete(brokenChain.blockm, brokenChain.chain[missing])
+	delete(brokenChain.receiptm, brokenChain.chain[missing])
+	tester.newPeer("faulty", protocol, brokenChain)
 
 	pending := new(sync.WaitGroup)
 	pending.Add(1)
-
 	go func() {
 		defer pending.Done()
 		if err := tester.sync("faulty", nil, mode); err == nil {
@@ -1550,16 +1277,17 @@ func testFailedSyncProgress(t *testing.T, protocol int, mode SyncMode) {
 		}
 	}()
 	<-starting
-	if progress := tester.downloader.Progress(); progress.StartingBlock != 0 || progress.CurrentBlock != 0 || progress.HighestBlock != uint64(targetBlocks) {
-		t.Fatalf("Initial progress mismatch: have %v/%v/%v, want %v/%v/%v", progress.StartingBlock, progress.CurrentBlock, progress.HighestBlock, 0, 0, targetBlocks)
-	}
+	checkProgress(t, tester.downloader, "initial", ethereum.SyncProgress{
+		HighestBlock: uint64(brokenChain.len() - 1),
+	})
 	progress <- struct{}{}
 	pending.Wait()
+	afterFailedSync := tester.downloader.Progress()
 
-	// Synchronise with a good peer and check that the progress origin remind the same after a failure
-	tester.newPeer("valid", protocol, hashes, headers, blocks, receipts)
+	// Synchronise with a good peer and check that the progress origin remind the same
+	// after a failure
+	tester.newPeer("valid", protocol, chain)
 	pending.Add(1)
-
 	go func() {
 		defer pending.Done()
 		if err := tester.sync("valid", nil, mode); err != nil {
@@ -1567,16 +1295,15 @@ func testFailedSyncProgress(t *testing.T, protocol int, mode SyncMode) {
 		}
 	}()
 	<-starting
-	if progress := tester.downloader.Progress(); progress.StartingBlock != 0 || progress.CurrentBlock > uint64(targetBlocks/2) || progress.HighestBlock != uint64(targetBlocks) {
-		t.Fatalf("Completing progress mismatch: have %v/%v/%v, want %v/0-%v/%v", progress.StartingBlock, progress.CurrentBlock, progress.HighestBlock, 0, targetBlocks/2, targetBlocks)
-	}
-	progress <- struct{}{}
-	pending.Wait()
+	checkProgress(t, tester.downloader, "completing", afterFailedSync)
 
 	// Check final progress after successful sync
-	if progress := tester.downloader.Progress(); progress.StartingBlock > uint64(targetBlocks/2) || progress.CurrentBlock != uint64(targetBlocks) || progress.HighestBlock != uint64(targetBlocks) {
-		t.Fatalf("Final progress mismatch: have %v/%v/%v, want 0-%v/%v/%v", progress.StartingBlock, progress.CurrentBlock, progress.HighestBlock, targetBlocks/2, targetBlocks, targetBlocks)
-	}
+	progress <- struct{}{}
+	pending.Wait()
+	checkProgress(t, tester.downloader, "final", ethereum.SyncProgress{
+		CurrentBlock: uint64(chain.len() - 1),
+		HighestBlock: uint64(chain.len() - 1),
+	})
 }
 
 // Tests that if an attacker fakes a chain height, after the attack is detected,
@@ -1593,34 +1320,27 @@ func testFakedSyncProgress(t *testing.T, protocol int, mode SyncMode) {
 
 	tester := newTester()
 	defer tester.terminate()
-
-	// Create a small block chain
-	targetBlocks := blockCacheItems - 15
-	hashes, headers, blocks, receipts := tester.makeChain(targetBlocks+3, 0, tester.genesis, nil, false)
+	chain := testChainBase.shorten(blockCacheItems - 15)
 
 	// Set a sync init hook to catch progress changes
 	starting := make(chan struct{})
 	progress := make(chan struct{})
-
 	tester.downloader.syncInitHook = func(origin, latest uint64) {
 		starting <- struct{}{}
 		<-progress
 	}
-	// Retrieve the sync progress and ensure they are zero (pristine sync)
-	if progress := tester.downloader.Progress(); progress.StartingBlock != 0 || progress.CurrentBlock != 0 || progress.HighestBlock != 0 {
-		t.Fatalf("Pristine progress mismatch: have %v/%v/%v, want %v/%v/%v", progress.StartingBlock, progress.CurrentBlock, progress.HighestBlock, 0, 0, 0)
-	}
-	//  Create and sync with an attacker that promises a higher chain than available
-	tester.newPeer("attack", protocol, hashes, headers, blocks, receipts)
-	for i := 1; i < 3; i++ {
-		delete(tester.peerHeaders["attack"], hashes[i])
-		delete(tester.peerBlocks["attack"], hashes[i])
-		delete(tester.peerReceipts["attack"], hashes[i])
+	checkProgress(t, tester.downloader, "pristine", ethereum.SyncProgress{})
+
+	// Create and sync with an attacker that promises a higher chain than available.
+	brokenChain := chain.shorten(chain.len())
+	numMissing := 5
+	for i := brokenChain.len() - 2; i > brokenChain.len()-numMissing; i-- {
+		delete(brokenChain.headerm, brokenChain.chain[i])
 	}
+	tester.newPeer("attack", protocol, brokenChain)
 
 	pending := new(sync.WaitGroup)
 	pending.Add(1)
-
 	go func() {
 		defer pending.Done()
 		if err := tester.sync("attack", nil, mode); err == nil {
@@ -1628,14 +1348,17 @@ func testFakedSyncProgress(t *testing.T, protocol int, mode SyncMode) {
 		}
 	}()
 	<-starting
-	if progress := tester.downloader.Progress(); progress.StartingBlock != 0 || progress.CurrentBlock != 0 || progress.HighestBlock != uint64(targetBlocks+3) {
-		t.Fatalf("Initial progress mismatch: have %v/%v/%v, want %v/%v/%v", progress.StartingBlock, progress.CurrentBlock, progress.HighestBlock, 0, 0, targetBlocks+3)
-	}
+	checkProgress(t, tester.downloader, "initial", ethereum.SyncProgress{
+		HighestBlock: uint64(brokenChain.len() - 1),
+	})
 	progress <- struct{}{}
 	pending.Wait()
+	afterFailedSync := tester.downloader.Progress()
 
-	// Synchronise with a good peer and check that the progress height has been reduced to the true value
-	tester.newPeer("valid", protocol, hashes[3:], headers, blocks, receipts)
+	// Synchronise with a good peer and check that the progress height has been reduced to
+	// the true value.
+	validChain := chain.shorten(chain.len() - numMissing)
+	tester.newPeer("valid", protocol, validChain)
 	pending.Add(1)
 
 	go func() {
@@ -1645,23 +1368,25 @@ func testFakedSyncProgress(t *testing.T, protocol int, mode SyncMode) {
 		}
 	}()
 	<-starting
-	if progress := tester.downloader.Progress(); progress.StartingBlock != 0 || progress.CurrentBlock > uint64(targetBlocks) || progress.HighestBlock != uint64(targetBlocks) {
-		t.Fatalf("Completing progress mismatch: have %v/%v/%v, want %v/0-%v/%v", progress.StartingBlock, progress.CurrentBlock, progress.HighestBlock, 0, targetBlocks, targetBlocks)
-	}
+	checkProgress(t, tester.downloader, "completing", ethereum.SyncProgress{
+		CurrentBlock: afterFailedSync.CurrentBlock,
+		HighestBlock: uint64(validChain.len() - 1),
+	})
+
+	// Check final progress after successful sync.
 	progress <- struct{}{}
 	pending.Wait()
-
-	// Check final progress after successful sync
-	if progress := tester.downloader.Progress(); progress.StartingBlock > uint64(targetBlocks) || progress.CurrentBlock != uint64(targetBlocks) || progress.HighestBlock != uint64(targetBlocks) {
-		t.Fatalf("Final progress mismatch: have %v/%v/%v, want 0-%v/%v/%v", progress.StartingBlock, progress.CurrentBlock, progress.HighestBlock, targetBlocks, targetBlocks, targetBlocks)
-	}
+	checkProgress(t, tester.downloader, "final", ethereum.SyncProgress{
+		CurrentBlock: uint64(validChain.len() - 1),
+		HighestBlock: uint64(validChain.len() - 1),
+	})
 }
 
 // This test reproduces an issue where unexpected deliveries would
 // block indefinitely if they arrived at the right time.
-// We use data driven subtests to manage this so that it will be parallel on its own
-// and not with the other tests, avoiding intermittent failures.
 func TestDeliverHeadersHang(t *testing.T) {
+	t.Parallel()
+
 	testCases := []struct {
 		protocol int
 		syncMode SyncMode
@@ -1675,15 +1400,38 @@ func TestDeliverHeadersHang(t *testing.T) {
 	}
 	for _, tc := range testCases {
 		t.Run(fmt.Sprintf("protocol %d mode %v", tc.protocol, tc.syncMode), func(t *testing.T) {
+			t.Parallel()
 			testDeliverHeadersHang(t, tc.protocol, tc.syncMode)
 		})
 	}
 }
 
+func testDeliverHeadersHang(t *testing.T, protocol int, mode SyncMode) {
+	master := newTester()
+	defer master.terminate()
+	chain := testChainBase.shorten(15)
+
+	for i := 0; i < 200; i++ {
+		tester := newTester()
+		tester.peerDb = master.peerDb
+		tester.newPeer("peer", protocol, chain)
+
+		// Whenever the downloader requests headers, flood it with
+		// a lot of unrequested header deliveries.
+		tester.downloader.peers.peers["peer"].peer = &floodingTestPeer{
+			peer:   tester.downloader.peers.peers["peer"].peer,
+			tester: tester,
+		}
+		if err := tester.sync("peer", nil, mode); err != nil {
+			t.Errorf("test %d: sync failed: %v", i, err)
+		}
+		tester.terminate()
+	}
+}
+
 type floodingTestPeer struct {
 	peer   Peer
 	tester *downloadTester
-	pend   sync.WaitGroup
 }
 
 func (ftp *floodingTestPeer) Head() (common.Hash, *big.Int) { return ftp.peer.Head() }
@@ -1702,54 +1450,32 @@ func (ftp *floodingTestPeer) RequestNodeData(hashes []common.Hash) error {
 
 func (ftp *floodingTestPeer) RequestHeadersByNumber(from uint64, count, skip int, reverse bool) error {
 	deliveriesDone := make(chan struct{}, 500)
-	for i := 0; i < cap(deliveriesDone); i++ {
+	for i := 0; i < cap(deliveriesDone)-1; i++ {
 		peer := fmt.Sprintf("fake-peer%d", i)
-		ftp.pend.Add(1)
-
 		go func() {
 			ftp.tester.downloader.DeliverHeaders(peer, []*types.Header{{}, {}, {}, {}})
 			deliveriesDone <- struct{}{}
-			ftp.pend.Done()
 		}()
 	}
-	// Deliver the actual requested headers.
-	go ftp.peer.RequestHeadersByNumber(from, count, skip, reverse)
+
 	// None of the extra deliveries should block.
 	timeout := time.After(60 * time.Second)
+	launched := false
 	for i := 0; i < cap(deliveriesDone); i++ {
 		select {
 		case <-deliveriesDone:
+			if !launched {
+				// Start delivering the requested headers
+				// after one of the flooding responses has arrived.
+				go func() {
+					ftp.peer.RequestHeadersByNumber(from, count, skip, reverse)
+					deliveriesDone <- struct{}{}
+				}()
+				launched = true
+			}
 		case <-timeout:
 			panic("blocked")
 		}
 	}
 	return nil
 }
-
-func testDeliverHeadersHang(t *testing.T, protocol int, mode SyncMode) {
-	t.Parallel()
-
-	master := newTester()
-	defer master.terminate()
-
-	hashes, headers, blocks, receipts := master.makeChain(5, 0, master.genesis, nil, false)
-	for i := 0; i < 200; i++ {
-		tester := newTester()
-		tester.peerDb = master.peerDb
-
-		tester.newPeer("peer", protocol, hashes, headers, blocks, receipts)
-		// Whenever the downloader requests headers, flood it with
-		// a lot of unrequested header deliveries.
-		tester.downloader.peers.peers["peer"].peer = &floodingTestPeer{
-			peer:   tester.downloader.peers.peers["peer"].peer,
-			tester: tester,
-		}
-		if err := tester.sync("peer", nil, mode); err != nil {
-			t.Errorf("test %d: sync failed: %v", i, err)
-		}
-		tester.terminate()
-
-		// Flush all goroutines to prevent messing with subsequent tests
-		tester.downloader.peers.peers["peer"].peer.(*floodingTestPeer).pend.Wait()
-	}
-}
diff --git a/eth/downloader/testchain_test.go b/eth/downloader/testchain_test.go
new file mode 100644
index 000000000..0b5a21425
--- /dev/null
+++ b/eth/downloader/testchain_test.go
@@ -0,0 +1,221 @@
+// Copyright 2018 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package downloader
+
+import (
+	"fmt"
+	"math/big"
+	"sync"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/consensus/ethash"
+	"github.com/ethereum/go-ethereum/core"
+	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/crypto"
+	"github.com/ethereum/go-ethereum/ethdb"
+	"github.com/ethereum/go-ethereum/params"
+)
+
+// Test chain parameters.
+var (
+	testKey, _  = crypto.HexToECDSA("b71c71a67e1177ad4e901695e1b4b9ee17ae16c6668d313eac2f96dbcda3f291")
+	testAddress = crypto.PubkeyToAddress(testKey.PublicKey)
+	testDB      = ethdb.NewMemDatabase()
+	testGenesis = core.GenesisBlockForTesting(testDB, testAddress, big.NewInt(1000000000))
+)
+
+// The common prefix of all test chains:
+var testChainBase = newTestChain(blockCacheItems+200, testGenesis)
+
+// Different forks on top of the base chain:
+var testChainForkLightA, testChainForkLightB, testChainForkHeavy *testChain
+
+func init() {
+	var forkLen = int(MaxForkAncestry + 50)
+	var wg sync.WaitGroup
+	wg.Add(3)
+	go func() { testChainForkLightA = testChainBase.makeFork(forkLen, false, 1); wg.Done() }()
+	go func() { testChainForkLightB = testChainBase.makeFork(forkLen, false, 2); wg.Done() }()
+	go func() { testChainForkHeavy = testChainBase.makeFork(forkLen, true, 3); wg.Done() }()
+	wg.Wait()
+}
+
+type testChain struct {
+	genesis  *types.Block
+	chain    []common.Hash
+	headerm  map[common.Hash]*types.Header
+	blockm   map[common.Hash]*types.Block
+	receiptm map[common.Hash][]*types.Receipt
+	tdm      map[common.Hash]*big.Int
+}
+
+// newTestChain creates a blockchain of the given length.
+func newTestChain(length int, genesis *types.Block) *testChain {
+	tc := new(testChain).copy(length)
+	tc.genesis = genesis
+	tc.chain = append(tc.chain, genesis.Hash())
+	tc.headerm[tc.genesis.Hash()] = tc.genesis.Header()
+	tc.tdm[tc.genesis.Hash()] = tc.genesis.Difficulty()
+	tc.blockm[tc.genesis.Hash()] = tc.genesis
+	tc.generate(length-1, 0, genesis, false)
+	return tc
+}
+
+// makeFork creates a fork on top of the test chain.
+func (tc *testChain) makeFork(length int, heavy bool, seed byte) *testChain {
+	fork := tc.copy(tc.len() + length)
+	fork.generate(length, seed, tc.headBlock(), heavy)
+	return fork
+}
+
+// shorten creates a copy of the chain with the given length. It panics if the
+// length is longer than the number of available blocks.
+func (tc *testChain) shorten(length int) *testChain {
+	if length > tc.len() {
+		panic(fmt.Errorf("can't shorten test chain to %d blocks, it's only %d blocks long", length, tc.len()))
+	}
+	return tc.copy(length)
+}
+
+func (tc *testChain) copy(newlen int) *testChain {
+	cpy := &testChain{
+		genesis:  tc.genesis,
+		headerm:  make(map[common.Hash]*types.Header, newlen),
+		blockm:   make(map[common.Hash]*types.Block, newlen),
+		receiptm: make(map[common.Hash][]*types.Receipt, newlen),
+		tdm:      make(map[common.Hash]*big.Int, newlen),
+	}
+	for i := 0; i < len(tc.chain) && i < newlen; i++ {
+		hash := tc.chain[i]
+		cpy.chain = append(cpy.chain, tc.chain[i])
+		cpy.tdm[hash] = tc.tdm[hash]
+		cpy.blockm[hash] = tc.blockm[hash]
+		cpy.headerm[hash] = tc.headerm[hash]
+		cpy.receiptm[hash] = tc.receiptm[hash]
+	}
+	return cpy
+}
+
+// generate creates a chain of n blocks starting at and including parent.
+// the returned hash chain is ordered head->parent. In addition, every 22th block
+// contains a transaction and every 5th an uncle to allow testing correct block
+// reassembly.
+func (tc *testChain) generate(n int, seed byte, parent *types.Block, heavy bool) {
+	// start := time.Now()
+	// defer func() { fmt.Printf("test chain generated in %v\n", time.Since(start)) }()
+
+	blocks, receipts := core.GenerateChain(params.TestChainConfig, parent, ethash.NewFaker(), testDB, n, func(i int, block *core.BlockGen) {
+		block.SetCoinbase(common.Address{seed})
+		// If a heavy chain is requested, delay blocks to raise difficulty
+		if heavy {
+			block.OffsetTime(-1)
+		}
+		// Include transactions to the miner to make blocks more interesting.
+		if parent == tc.genesis && i%22 == 0 {
+			signer := types.MakeSigner(params.TestChainConfig, block.Number())
+			tx, err := types.SignTx(types.NewTransaction(block.TxNonce(testAddress), common.Address{seed}, big.NewInt(1000), params.TxGas, nil, nil), signer, testKey)
+			if err != nil {
+				panic(err)
+			}
+			block.AddTx(tx)
+		}
+		// if the block number is a multiple of 5, add a bonus uncle to the block
+		if i > 0 && i%5 == 0 {
+			block.AddUncle(&types.Header{
+				ParentHash: block.PrevBlock(i - 1).Hash(),
+				Number:     big.NewInt(block.Number().Int64() - 1),
+			})
+		}
+	})
+
+	// Convert the block-chain into a hash-chain and header/block maps
+	td := new(big.Int).Set(tc.td(parent.Hash()))
+	for i, b := range blocks {
+		td := td.Add(td, b.Difficulty())
+		hash := b.Hash()
+		tc.chain = append(tc.chain, hash)
+		tc.blockm[hash] = b
+		tc.headerm[hash] = b.Header()
+		tc.receiptm[hash] = receipts[i]
+		tc.tdm[hash] = new(big.Int).Set(td)
+	}
+}
+
+// len returns the total number of blocks in the chain.
+func (tc *testChain) len() int {
+	return len(tc.chain)
+}
+
+// headBlock returns the head of the chain.
+func (tc *testChain) headBlock() *types.Block {
+	return tc.blockm[tc.chain[len(tc.chain)-1]]
+}
+
+// td returns the total difficulty of the given block.
+func (tc *testChain) td(hash common.Hash) *big.Int {
+	return tc.tdm[hash]
+}
+
+// headersByHash returns headers in ascending order from the given hash.
+func (tc *testChain) headersByHash(origin common.Hash, amount int, skip int) []*types.Header {
+	num, _ := tc.hashToNumber(origin)
+	return tc.headersByNumber(num, amount, skip)
+}
+
+// headersByNumber returns headers in ascending order from the given number.
+func (tc *testChain) headersByNumber(origin uint64, amount int, skip int) []*types.Header {
+	result := make([]*types.Header, 0, amount)
+	for num := origin; num < uint64(len(tc.chain)) && len(result) < amount; num += uint64(skip) + 1 {
+		if header, ok := tc.headerm[tc.chain[int(num)]]; ok {
+			result = append(result, header)
+		}
+	}
+	return result
+}
+
+// receipts returns the receipts of the given block hashes.
+func (tc *testChain) receipts(hashes []common.Hash) [][]*types.Receipt {
+	results := make([][]*types.Receipt, 0, len(hashes))
+	for _, hash := range hashes {
+		if receipt, ok := tc.receiptm[hash]; ok {
+			results = append(results, receipt)
+		}
+	}
+	return results
+}
+
+// bodies returns the block bodies of the given block hashes.
+func (tc *testChain) bodies(hashes []common.Hash) ([][]*types.Transaction, [][]*types.Header) {
+	transactions := make([][]*types.Transaction, 0, len(hashes))
+	uncles := make([][]*types.Header, 0, len(hashes))
+	for _, hash := range hashes {
+		if block, ok := tc.blockm[hash]; ok {
+			transactions = append(transactions, block.Transactions())
+			uncles = append(uncles, block.Uncles())
+		}
+	}
+	return transactions, uncles
+}
+
+func (tc *testChain) hashToNumber(target common.Hash) (uint64, bool) {
+	for num, hash := range tc.chain {
+		if hash == target {
+			return uint64(num), true
+		}
+	}
+	return 0, false
+}