Add combinatorial tests for internal Exchange functions (#807)

* WIP add combinatorial tests for internal Exchange functions

* Change combinitorial testing strategy based on feedback

* Check value of filled[orderHash] in updateFilledState tests

* Add combinatorial tests for addFillResults

* Add combinatorial tests for getPartialAmount

* Implement generic `testWithReferenceFuncAsync`

* Implement generic `testCombinatoriallyWithReferenceFuncAsync`

* Add combinatorial tests for isRoundingError

* Add combinatorial tests for calculateFillResults

* Add support for Geth in internal contract tests

* Fix contract artifacts

* Change DECIMAL_PLACES to 78 and add a note.

* Document new functions in utils

* Optimize tests by only reseting state when needed

* Rename/move some files

* Print parameter names on failure in testWithReferenceFuncAsync

* Add to changelog for utils package

* Appease various linters

* Rename some more things related to FillOrderCombinatorialUtils

* Remove .only from test/exchange/internal.ts

* Remove old test for isRoundingError and getPartialAmount

* Appease linters again

* Remove old todos

* Fix typos, add comments, rename some things

* Re-add some LibMath tests

* Update contract internal tests to use new SafeMath revert reasons

* Apply PR feedback from Amir

* Apply PR feedback from Remco

* Re-add networks to ZRXToken artifact

* Remove duplicate Whitelist in compiler.json

12 files changed, 756 insertions, 128 deletions

diff --git a/packages/contracts/compiler.json b/packages/contracts/compiler.json
index dba836bde..ad35fc5b3 100644
--- a/packages/contracts/compiler.json
+++ b/packages/contracts/compiler.json
@@ -42,12 +42,13 @@
         "TestConstants",
         "TestLibBytes",
         "TestLibs",
+        "TestExchangeInternals",
         "TestSignatureValidator",
         "TokenRegistry",
         "Validator",
         "Wallet",
-        "Whitelist",
         "WETH9",
+        "Whitelist",
         "ZRXToken"
     ]
 }
diff --git a/packages/contracts/package.json b/packages/contracts/package.json
index 9fe8046b1..014210d33 100644
--- a/packages/contracts/package.json
+++ b/packages/contracts/package.json
@@ -33,7 +33,7 @@
         "lint-contracts": "solhint src/2.0.0/**/**/**/**/*.sol"
     },
     "config": {
-        "abis": "../migrations/artifacts/2.0.0/@(AssetProxyOwner|DummyERC20Token|DummyERC721Receiver|DummyERC721Token|ERC20Proxy|ERC721Proxy|Forwarder|Exchange|ExchangeWrapper|IAssetData|IAssetProxy|MixinAuthorizable|MultiSigWallet|MultiSigWalletWithTimeLock|TestAssetProxyOwner|TestAssetProxyDispatcher|TestConstants|TestLibBytes|TestLibs|TestSignatureValidator|Validator|Wallet|TokenRegistry|Whitelist|WETH9|ZRXToken).json"
+        "abis": "../migrations/artifacts/2.0.0/@(AssetProxyOwner|DummyERC20Token|DummyERC721Receiver|DummyERC721Token|ERC20Proxy|ERC721Proxy|Forwarder|Exchange|ExchangeWrapper|IAssetData|IAssetProxy|MixinAuthorizable|MultiSigWallet|MultiSigWalletWithTimeLock|TestAssetProxyOwner|TestAssetProxyDispatcher|TestConstants|TestExchangeInternals|TestLibBytes|TestLibs|TestSignatureValidator|Validator|Wallet|TokenRegistry|Whitelist|WETH9|ZRXToken).json"
     },
     "repository": {
         "type": "git",
@@ -79,11 +79,13 @@
         "@0xproject/typescript-typings": "^1.0.3",
         "@0xproject/utils": "^1.0.4",
         "@0xproject/web3-wrapper": "^1.1.2",
+        "@types/js-combinatorics": "^0.5.29",
         "bn.js": "^4.11.8",
         "ethereum-types": "^1.0.3",
         "ethereumjs-abi": "0.6.5",
         "ethereumjs-util": "^5.1.1",
         "ethers": "3.0.22",
+        "js-combinatorics": "^0.5.3",
         "lodash": "^4.17.4"
     }
 }
diff --git a/packages/contracts/src/2.0.0/protocol/Exchange/MixinExchangeCore.sol b/packages/contracts/src/2.0.0/protocol/Exchange/MixinExchangeCore.sol
index 354d0e9c3..ab5c6e507 100644
--- a/packages/contracts/src/2.0.0/protocol/Exchange/MixinExchangeCore.sol
+++ b/packages/contracts/src/2.0.0/protocol/Exchange/MixinExchangeCore.sol
@@ -207,7 +207,6 @@ contract MixinExchangeCore is
     /// @param order that was filled.
     /// @param takerAddress Address of taker who filled the order.
     /// @param orderTakerAssetFilledAmount Amount of order already filled.
-    /// @return fillResults Amounts filled and fees paid by maker and taker.
     function updateFilledState(
         Order memory order,
         address takerAddress,
diff --git a/packages/contracts/src/2.0.0/test/TestExchangeInternals/TestExchangeInternals.sol b/packages/contracts/src/2.0.0/test/TestExchangeInternals/TestExchangeInternals.sol
new file mode 100644
index 000000000..923bac97d
--- /dev/null
+++ b/packages/contracts/src/2.0.0/test/TestExchangeInternals/TestExchangeInternals.sol
@@ -0,0 +1,120 @@
+/*
+
+  Copyright 2018 ZeroEx Intl.
+
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+
+*/
+
+pragma solidity 0.4.24;
+pragma experimental ABIEncoderV2;
+
+import "../../protocol/Exchange/Exchange.sol";
+
+
+contract TestExchangeInternals is
+    Exchange
+{
+    constructor ()
+        public
+        Exchange("")
+    {}
+
+    /// @dev Adds properties of both FillResults instances.
+    ///      Modifies the first FillResults instance specified.
+    ///      Note that this function has been modified from the original
+    //       internal version to return the FillResults.
+    /// @param totalFillResults Fill results instance that will be added onto.
+    /// @param singleFillResults Fill results instance that will be added to totalFillResults.
+    /// @return newTotalFillResults The result of adding singleFillResults to totalFilResults.
+    function publicAddFillResults(FillResults memory totalFillResults, FillResults memory singleFillResults)
+        public
+        pure
+        returns (FillResults memory)
+    {
+        addFillResults(totalFillResults, singleFillResults);
+        return totalFillResults;
+    }
+
+    /// @dev Calculates amounts filled and fees paid by maker and taker.
+    /// @param order to be filled.
+    /// @param takerAssetFilledAmount Amount of takerAsset that will be filled.
+    /// @return fillResults Amounts filled and fees paid by maker and taker.
+    function publicCalculateFillResults(
+        Order memory order,
+        uint256 takerAssetFilledAmount
+    )
+        public
+        pure
+        returns (FillResults memory fillResults)
+    {
+        return calculateFillResults(order, takerAssetFilledAmount);
+    }
+
+    /// @dev Calculates partial value given a numerator and denominator.
+    /// @param numerator Numerator.
+    /// @param denominator Denominator.
+    /// @param target Value to calculate partial of.
+    /// @return Partial value of target.
+    function publicGetPartialAmount(
+        uint256 numerator,
+        uint256 denominator,
+        uint256 target
+    )
+        public
+        pure
+        returns (uint256 partialAmount)
+    {
+        return getPartialAmount(numerator, denominator, target);
+    }
+
+    /// @dev Checks if rounding error > 0.1%.
+    /// @param numerator Numerator.
+    /// @param denominator Denominator.
+    /// @param target Value to multiply with numerator/denominator.
+    /// @return Rounding error is present.
+    function publicIsRoundingError(
+        uint256 numerator,
+        uint256 denominator,
+        uint256 target
+    )
+        public
+        pure
+        returns (bool isError)
+    {
+        return isRoundingError(numerator, denominator, target);
+    }
+ 
+    /// @dev Updates state with results of a fill order.
+    /// @param order that was filled.
+    /// @param takerAddress Address of taker who filled the order.
+    /// @param orderTakerAssetFilledAmount Amount of order already filled.
+    /// @return fillResults Amounts filled and fees paid by maker and taker.
+    function publicUpdateFilledState(
+        Order memory order,
+        address takerAddress,
+        bytes32 orderHash,
+        uint256 orderTakerAssetFilledAmount,
+        FillResults memory fillResults
+    )
+        public
+    {
+        updateFilledState(
+            order,
+            takerAddress,
+            orderHash,
+            orderTakerAssetFilledAmount,
+            fillResults
+        );
+    }
+}
diff --git a/packages/contracts/test/exchange/fill_order.ts b/packages/contracts/test/exchange/fill_order.ts
index 029bd66e2..1494fe093 100644
--- a/packages/contracts/test/exchange/fill_order.ts
+++ b/packages/contracts/test/exchange/fill_order.ts
@@ -2,7 +2,10 @@ import { BlockchainLifecycle } from '@0xproject/dev-utils';
 import * as _ from 'lodash';
 
 import { chaiSetup } from '../utils/chai_setup';
-import { CoreCombinatorialUtils, coreCombinatorialUtilsFactoryAsync } from '../utils/core_combinatorial_utils';
+import {
+    FillOrderCombinatorialUtils,
+    fillOrderCombinatorialUtilsFactoryAsync,
+} from '../utils/fill_order_combinatorial_utils';
 import {
     AllowanceAmountScenario,
     AssetDataScenario,
@@ -47,11 +50,11 @@ const defaultFillScenario = {
 };
 
 describe('FillOrder Tests', () => {
-    let coreCombinatorialUtils: CoreCombinatorialUtils;
+    let fillOrderCombinatorialUtils: FillOrderCombinatorialUtils;
 
     before(async () => {
         await blockchainLifecycle.startAsync();
-        coreCombinatorialUtils = await coreCombinatorialUtilsFactoryAsync(web3Wrapper, txDefaults);
+        fillOrderCombinatorialUtils = await fillOrderCombinatorialUtilsFactoryAsync(web3Wrapper, txDefaults);
     });
     after(async () => {
         await blockchainLifecycle.revertAsync();
@@ -67,19 +70,19 @@ describe('FillOrder Tests', () => {
             _.forEach(fillScenarios, fillScenario => {
                 const description = `Combinatorial OrderFill: ${JSON.stringify(fillScenario)}`;
                 it(description, async () => {
-                    await coreCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
+                    await fillOrderCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
                 });
             });
         };
 
-        const allFillScenarios = CoreCombinatorialUtils.generateFillOrderCombinations();
+        const allFillScenarios = FillOrderCombinatorialUtils.generateFillOrderCombinations();
         describe('Combinatorially generated fills orders', () => test(allFillScenarios));
 
         it('should transfer the correct amounts when makerAssetAmount === takerAssetAmount', async () => {
             const fillScenario = {
                 ...defaultFillScenario,
             };
-            await coreCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
+            await fillOrderCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
         });
         it('should transfer the correct amounts when makerAssetAmount > takerAssetAmount', async () => {
             const fillScenario = {
@@ -89,7 +92,7 @@ describe('FillOrder Tests', () => {
                     takerAssetAmountScenario: OrderAssetAmountScenario.Small,
                 },
             };
-            await coreCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
+            await fillOrderCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
         });
         it('should transfer the correct amounts when makerAssetAmount < takerAssetAmount', async () => {
             const fillScenario = {
@@ -99,7 +102,7 @@ describe('FillOrder Tests', () => {
                     makerAssetAmountScenario: OrderAssetAmountScenario.Small,
                 },
             };
-            await coreCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
+            await fillOrderCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
         });
         it('should transfer the correct amounts when taker is specified and order is claimed by taker', async () => {
             const fillScenario = {
@@ -109,14 +112,14 @@ describe('FillOrder Tests', () => {
                     takerScenario: TakerScenario.CorrectlySpecified,
                 },
             };
-            await coreCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
+            await fillOrderCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
         });
         it('should fill remaining value if takerAssetFillAmount > remaining takerAssetAmount', async () => {
             const fillScenario = {
                 ...defaultFillScenario,
                 takerAssetFillAmountScenario: TakerAssetFillAmountScenario.GreaterThanRemainingFillableTakerAssetAmount,
             };
-            await coreCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
+            await fillOrderCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
         });
         it('should throw when taker is specified and order is claimed by other', async () => {
             const fillScenario = {
@@ -126,7 +129,7 @@ describe('FillOrder Tests', () => {
                     takerScenario: TakerScenario.IncorrectlySpecified,
                 },
             };
-            await coreCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
+            await fillOrderCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
         });
 
         it('should throw if makerAssetAmount is 0', async () => {
@@ -138,7 +141,7 @@ describe('FillOrder Tests', () => {
                 },
                 takerAssetFillAmountScenario: TakerAssetFillAmountScenario.GreaterThanRemainingFillableTakerAssetAmount,
             };
-            await coreCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
+            await fillOrderCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
         });
 
         it('should throw if takerAssetAmount is 0', async () => {
@@ -150,7 +153,7 @@ describe('FillOrder Tests', () => {
                 },
                 takerAssetFillAmountScenario: TakerAssetFillAmountScenario.GreaterThanRemainingFillableTakerAssetAmount,
             };
-            await coreCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
+            await fillOrderCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
         });
 
         it('should throw if takerAssetFillAmount is 0', async () => {
@@ -158,7 +161,7 @@ describe('FillOrder Tests', () => {
                 ...defaultFillScenario,
                 takerAssetFillAmountScenario: TakerAssetFillAmountScenario.Zero,
             };
-            await coreCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
+            await fillOrderCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
         });
 
         it('should throw if an order is expired', async () => {
@@ -169,7 +172,7 @@ describe('FillOrder Tests', () => {
                     expirationTimeSecondsScenario: ExpirationTimeSecondsScenario.InPast,
                 },
             };
-            await coreCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
+            await fillOrderCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
         });
 
         it('should throw if maker erc20Balances are too low to fill order', async () => {
@@ -180,7 +183,7 @@ describe('FillOrder Tests', () => {
                     traderAssetBalance: BalanceAmountScenario.TooLow,
                 },
             };
-            await coreCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
+            await fillOrderCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
         });
 
         it('should throw if taker erc20Balances are too low to fill order', async () => {
@@ -191,7 +194,7 @@ describe('FillOrder Tests', () => {
                     traderAssetBalance: BalanceAmountScenario.TooLow,
                 },
             };
-            await coreCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
+            await fillOrderCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
         });
 
         it('should throw if maker allowances are too low to fill order', async () => {
@@ -202,7 +205,7 @@ describe('FillOrder Tests', () => {
                     traderAssetAllowance: AllowanceAmountScenario.TooLow,
                 },
             };
-            await coreCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
+            await fillOrderCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
         });
 
         it('should throw if taker allowances are too low to fill order', async () => {
@@ -213,7 +216,7 @@ describe('FillOrder Tests', () => {
                     traderAssetAllowance: AllowanceAmountScenario.TooLow,
                 },
             };
-            await coreCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
+            await fillOrderCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
         });
     });
 
@@ -228,7 +231,7 @@ describe('FillOrder Tests', () => {
                 },
                 takerAssetFillAmountScenario: TakerAssetFillAmountScenario.ExactlyRemainingFillableTakerAssetAmount,
             };
-            await coreCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
+            await fillOrderCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
         });
 
         it('should successfully fill order when makerAsset is ERC721 and takerAsset is ERC20', async () => {
@@ -241,7 +244,7 @@ describe('FillOrder Tests', () => {
                 },
                 takerAssetFillAmountScenario: TakerAssetFillAmountScenario.ExactlyRemainingFillableTakerAssetAmount,
             };
-            await coreCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario, true);
+            await fillOrderCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario, true);
         });
 
         it('should successfully fill order when makerAsset is ERC20 and takerAsset is ERC721', async () => {
@@ -254,7 +257,7 @@ describe('FillOrder Tests', () => {
                 },
                 takerAssetFillAmountScenario: TakerAssetFillAmountScenario.ExactlyRemainingFillableTakerAssetAmount,
             };
-            await coreCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
+            await fillOrderCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
         });
 
         it('should successfully fill order when makerAsset is ERC721 and approveAll is set for it', async () => {
@@ -271,7 +274,7 @@ describe('FillOrder Tests', () => {
                     traderAssetAllowance: AllowanceAmountScenario.Unlimited,
                 },
             };
-            await coreCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
+            await fillOrderCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
         });
 
         it('should successfully fill order when makerAsset and takerAsset are ERC721 and approveAll is set for them', async () => {
@@ -292,7 +295,7 @@ describe('FillOrder Tests', () => {
                     traderAssetAllowance: AllowanceAmountScenario.Unlimited,
                 },
             };
-            await coreCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
+            await fillOrderCombinatorialUtils.testFillOrderScenarioAsync(provider, fillScenario);
         });
     });
 });
diff --git a/packages/contracts/test/exchange/internal.ts b/packages/contracts/test/exchange/internal.ts
new file mode 100644
index 000000000..67d1d2d2c
--- /dev/null
+++ b/packages/contracts/test/exchange/internal.ts
@@ -0,0 +1,305 @@
+import { BlockchainLifecycle } from '@0xproject/dev-utils';
+import { Order, RevertReason, SignedOrder } from '@0xproject/types';
+import { BigNumber } from '@0xproject/utils';
+import * as _ from 'lodash';
+
+import { TestExchangeInternalsContract } from '../../generated_contract_wrappers/test_exchange_internals';
+import { artifacts } from '../utils/artifacts';
+import {
+    getInvalidOpcodeErrorMessageForCallAsync,
+    getRevertReasonOrErrorMessageForSendTransactionAsync,
+} from '../utils/assertions';
+import { chaiSetup } from '../utils/chai_setup';
+import { bytes32Values, testCombinatoriallyWithReferenceFuncAsync, uint256Values } from '../utils/combinatorial_utils';
+import { constants } from '../utils/constants';
+import { FillResults } from '../utils/types';
+import { provider, txDefaults, web3Wrapper } from '../utils/web3_wrapper';
+
+chaiSetup.configure();
+const blockchainLifecycle = new BlockchainLifecycle(web3Wrapper);
+
+const MAX_UINT256 = new BigNumber(2).pow(256).minus(1);
+
+const emptyOrder: Order = {
+    senderAddress: constants.NULL_ADDRESS,
+    makerAddress: constants.NULL_ADDRESS,
+    takerAddress: constants.NULL_ADDRESS,
+    makerFee: new BigNumber(0),
+    takerFee: new BigNumber(0),
+    makerAssetAmount: new BigNumber(0),
+    takerAssetAmount: new BigNumber(0),
+    makerAssetData: '0x',
+    takerAssetData: '0x',
+    salt: new BigNumber(0),
+    exchangeAddress: constants.NULL_ADDRESS,
+    feeRecipientAddress: constants.NULL_ADDRESS,
+    expirationTimeSeconds: new BigNumber(0),
+};
+
+const emptySignedOrder: SignedOrder = {
+    ...emptyOrder,
+    signature: '',
+};
+
+const overflowErrorForCall = new Error(RevertReason.Uint256Overflow);
+
+async function referenceGetPartialAmountAsync(
+    numerator: BigNumber,
+    denominator: BigNumber,
+    target: BigNumber,
+): Promise<BigNumber> {
+    const invalidOpcodeErrorForCall = new Error(await getInvalidOpcodeErrorMessageForCallAsync());
+    const product = numerator.mul(target);
+    if (product.greaterThan(MAX_UINT256)) {
+        throw overflowErrorForCall;
+    }
+    if (denominator.eq(0)) {
+        throw invalidOpcodeErrorForCall;
+    }
+    return product.dividedToIntegerBy(denominator);
+}
+
+describe('Exchange core internal functions', () => {
+    let testExchange: TestExchangeInternalsContract;
+    let invalidOpcodeErrorForCall: Error | undefined;
+    let overflowErrorForSendTransaction: Error | undefined;
+
+    before(async () => {
+        await blockchainLifecycle.startAsync();
+    });
+    after(async () => {
+        await blockchainLifecycle.revertAsync();
+    });
+    before(async () => {
+        testExchange = await TestExchangeInternalsContract.deployFrom0xArtifactAsync(
+            artifacts.TestExchangeInternals,
+            provider,
+            txDefaults,
+        );
+        overflowErrorForSendTransaction = new Error(
+            await getRevertReasonOrErrorMessageForSendTransactionAsync(RevertReason.Uint256Overflow),
+        );
+        invalidOpcodeErrorForCall = new Error(await getInvalidOpcodeErrorMessageForCallAsync());
+    });
+    // Note(albrow): Don't forget to add beforeEach and afterEach calls to reset
+    // the blockchain state for any tests which modify it!
+
+    describe('addFillResults', async () => {
+        function makeFillResults(value: BigNumber): FillResults {
+            return {
+                makerAssetFilledAmount: value,
+                takerAssetFilledAmount: value,
+                makerFeePaid: value,
+                takerFeePaid: value,
+            };
+        }
+        async function referenceAddFillResultsAsync(
+            totalValue: BigNumber,
+            singleValue: BigNumber,
+        ): Promise<FillResults> {
+            // Note(albrow): Here, each of totalFillResults and
+            // singleFillResults will consist of fields with the same values.
+            // This should be safe because none of the fields in a given
+            // FillResults are ever used together in a mathemetical operation.
+            // They are only used with the corresponding field from *the other*
+            // FillResults, which are different.
+            const totalFillResults = makeFillResults(totalValue);
+            const singleFillResults = makeFillResults(singleValue);
+            // HACK(albrow): _.mergeWith mutates the first argument! To
+            // workaround this we use _.cloneDeep.
+            return _.mergeWith(
+                _.cloneDeep(totalFillResults),
+                singleFillResults,
+                (totalVal: BigNumber, singleVal: BigNumber) => {
+                    const newTotal = totalVal.add(singleVal);
+                    if (newTotal.greaterThan(MAX_UINT256)) {
+                        throw overflowErrorForCall;
+                    }
+                    return newTotal;
+                },
+            );
+        }
+        async function testAddFillResultsAsync(totalValue: BigNumber, singleValue: BigNumber): Promise<FillResults> {
+            const totalFillResults = makeFillResults(totalValue);
+            const singleFillResults = makeFillResults(singleValue);
+            return testExchange.publicAddFillResults.callAsync(totalFillResults, singleFillResults);
+        }
+        await testCombinatoriallyWithReferenceFuncAsync(
+            'addFillResults',
+            referenceAddFillResultsAsync,
+            testAddFillResultsAsync,
+            [uint256Values, uint256Values],
+        );
+    });
+
+    describe('calculateFillResults', async () => {
+        function makeOrder(
+            makerAssetAmount: BigNumber,
+            takerAssetAmount: BigNumber,
+            makerFee: BigNumber,
+            takerFee: BigNumber,
+        ): Order {
+            return {
+                ...emptyOrder,
+                makerAssetAmount,
+                takerAssetAmount,
+                makerFee,
+                takerFee,
+            };
+        }
+        async function referenceCalculateFillResultsAsync(
+            orderTakerAssetAmount: BigNumber,
+            takerAssetFilledAmount: BigNumber,
+            otherAmount: BigNumber,
+        ): Promise<FillResults> {
+            // Note(albrow): Here we are re-using the same value (otherAmount)
+            // for order.makerAssetAmount, order.makerFee, and order.takerFee.
+            // This should be safe because they are never used with each other
+            // in any mathematical operation in either the reference TypeScript
+            // implementation or the Solidity implementation of
+            // calculateFillResults.
+            return {
+                makerAssetFilledAmount: await referenceGetPartialAmountAsync(
+                    takerAssetFilledAmount,
+                    orderTakerAssetAmount,
+                    otherAmount,
+                ),
+                takerAssetFilledAmount,
+                makerFeePaid: await referenceGetPartialAmountAsync(
+                    takerAssetFilledAmount,
+                    orderTakerAssetAmount,
+                    otherAmount,
+                ),
+                takerFeePaid: await referenceGetPartialAmountAsync(
+                    takerAssetFilledAmount,
+                    orderTakerAssetAmount,
+                    otherAmount,
+                ),
+            };
+        }
+        async function testCalculateFillResultsAsync(
+            orderTakerAssetAmount: BigNumber,
+            takerAssetFilledAmount: BigNumber,
+            otherAmount: BigNumber,
+        ): Promise<FillResults> {
+            const order = makeOrder(otherAmount, orderTakerAssetAmount, otherAmount, otherAmount);
+            return testExchange.publicCalculateFillResults.callAsync(order, takerAssetFilledAmount);
+        }
+        await testCombinatoriallyWithReferenceFuncAsync(
+            'calculateFillResults',
+            referenceCalculateFillResultsAsync,
+            testCalculateFillResultsAsync,
+            [uint256Values, uint256Values, uint256Values],
+        );
+    });
+
+    describe('getPartialAmount', async () => {
+        async function testGetPartialAmountAsync(
+            numerator: BigNumber,
+            denominator: BigNumber,
+            target: BigNumber,
+        ): Promise<BigNumber> {
+            return testExchange.publicGetPartialAmount.callAsync(numerator, denominator, target);
+        }
+        await testCombinatoriallyWithReferenceFuncAsync(
+            'getPartialAmount',
+            referenceGetPartialAmountAsync,
+            testGetPartialAmountAsync,
+            [uint256Values, uint256Values, uint256Values],
+        );
+    });
+
+    describe('isRoundingError', async () => {
+        async function referenceIsRoundingErrorAsync(
+            numerator: BigNumber,
+            denominator: BigNumber,
+            target: BigNumber,
+        ): Promise<boolean> {
+            const product = numerator.mul(target);
+            if (denominator.eq(0)) {
+                throw invalidOpcodeErrorForCall;
+            }
+            const remainder = product.mod(denominator);
+            if (remainder.eq(0)) {
+                return false;
+            }
+            if (product.greaterThan(MAX_UINT256)) {
+                throw overflowErrorForCall;
+            }
+            if (product.eq(0)) {
+                throw invalidOpcodeErrorForCall;
+            }
+            const remainderTimes1000000 = remainder.mul('1000000');
+            if (remainderTimes1000000.greaterThan(MAX_UINT256)) {
+                throw overflowErrorForCall;
+            }
+            const errPercentageTimes1000000 = remainderTimes1000000.dividedToIntegerBy(product);
+            return errPercentageTimes1000000.greaterThan('1000');
+        }
+        async function testIsRoundingErrorAsync(
+            numerator: BigNumber,
+            denominator: BigNumber,
+            target: BigNumber,
+        ): Promise<boolean> {
+            return testExchange.publicIsRoundingError.callAsync(numerator, denominator, target);
+        }
+        await testCombinatoriallyWithReferenceFuncAsync(
+            'isRoundingError',
+            referenceIsRoundingErrorAsync,
+            testIsRoundingErrorAsync,
+            [uint256Values, uint256Values, uint256Values],
+        );
+    });
+
+    describe('updateFilledState', async () => {
+        // Note(albrow): Since updateFilledState modifies the state by calling
+        // sendTransaction, we must reset the state after each test.
+        beforeEach(async () => {
+            await blockchainLifecycle.startAsync();
+        });
+        afterEach(async () => {
+            await blockchainLifecycle.revertAsync();
+        });
+        async function referenceUpdateFilledStateAsync(
+            takerAssetFilledAmount: BigNumber,
+            orderTakerAssetFilledAmount: BigNumber,
+            // tslint:disable-next-line:no-unused-variable
+            orderHash: string,
+        ): Promise<BigNumber> {
+            const totalFilledAmount = takerAssetFilledAmount.add(orderTakerAssetFilledAmount);
+            if (totalFilledAmount.greaterThan(MAX_UINT256)) {
+                throw overflowErrorForSendTransaction;
+            }
+            return totalFilledAmount;
+        }
+        async function testUpdateFilledStateAsync(
+            takerAssetFilledAmount: BigNumber,
+            orderTakerAssetFilledAmount: BigNumber,
+            orderHash: string,
+        ): Promise<BigNumber> {
+            const fillResults = {
+                makerAssetFilledAmount: new BigNumber(0),
+                takerAssetFilledAmount,
+                makerFeePaid: new BigNumber(0),
+                takerFeePaid: new BigNumber(0),
+            };
+            await web3Wrapper.awaitTransactionSuccessAsync(
+                await testExchange.publicUpdateFilledState.sendTransactionAsync(
+                    emptySignedOrder,
+                    constants.NULL_ADDRESS,
+                    orderHash,
+                    orderTakerAssetFilledAmount,
+                    fillResults,
+                ),
+                constants.AWAIT_TRANSACTION_MINED_MS,
+            );
+            return testExchange.filled.callAsync(orderHash);
+        }
+        await testCombinatoriallyWithReferenceFuncAsync(
+            'updateFilledState',
+            referenceUpdateFilledStateAsync,
+            testUpdateFilledStateAsync,
+            [uint256Values, uint256Values, bytes32Values],
+        );
+    });
+});
diff --git a/packages/contracts/test/exchange/libs.ts b/packages/contracts/test/exchange/libs.ts
index 51794d8a3..5c9f9aac7 100644
--- a/packages/contracts/test/exchange/libs.ts
+++ b/packages/contracts/test/exchange/libs.ts
@@ -67,6 +67,35 @@ describe('Exchange libs', () => {
             });
         });
     });
+    // Note(albrow): These tests are designed to be supplemental to the
+    // combinatorial tests in test/exchange/internal. They test specific edge
+    // cases that are not covered by the combinatorial tests.
+    describe('LibMath', () => {
+        it('should return false if there is a rounding error of 0.1%', async () => {
+            const numerator = new BigNumber(20);
+            const denominator = new BigNumber(999);
+            const target = new BigNumber(50);
+            // rounding error = ((20*50/999) - floor(20*50/999)) / (20*50/999) = 0.1%
+            const isRoundingError = await libs.publicIsRoundingError.callAsync(numerator, denominator, target);
+            expect(isRoundingError).to.be.false();
+        });
+        it('should return false if there is a rounding of 0.09%', async () => {
+            const numerator = new BigNumber(20);
+            const denominator = new BigNumber(9991);
+            const target = new BigNumber(500);
+            // rounding error = ((20*500/9991) - floor(20*500/9991)) / (20*500/9991) = 0.09%
+            const isRoundingError = await libs.publicIsRoundingError.callAsync(numerator, denominator, target);
+            expect(isRoundingError).to.be.false();
+        });
+        it('should return true if there is a rounding error of 0.11%', async () => {
+            const numerator = new BigNumber(20);
+            const denominator = new BigNumber(9989);
+            const target = new BigNumber(500);
+            // rounding error = ((20*500/9989) - floor(20*500/9989)) / (20*500/9989) = 0.011%
+            const isRoundingError = await libs.publicIsRoundingError.callAsync(numerator, denominator, target);
+            expect(isRoundingError).to.be.true();
+        });
+    });
 
     describe('LibOrder', () => {
         describe('getOrderSchema', () => {
@@ -93,96 +122,4 @@ describe('Exchange libs', () => {
             });
         });
     });
-
-    describe('LibMath', () => {
-        describe('isRoundingError', () => {
-            it('should return false if there is a rounding error of 0.1%', async () => {
-                const numerator = new BigNumber(20);
-                const denominator = new BigNumber(999);
-                const target = new BigNumber(50);
-                // rounding error = ((20*50/999) - floor(20*50/999)) / (20*50/999) = 0.1%
-                const isRoundingError = await libs.publicIsRoundingError.callAsync(numerator, denominator, target);
-                expect(isRoundingError).to.be.false();
-            });
-
-            it('should return false if there is a rounding of 0.09%', async () => {
-                const numerator = new BigNumber(20);
-                const denominator = new BigNumber(9991);
-                const target = new BigNumber(500);
-                // rounding error = ((20*500/9991) - floor(20*500/9991)) / (20*500/9991) = 0.09%
-                const isRoundingError = await libs.publicIsRoundingError.callAsync(numerator, denominator, target);
-                expect(isRoundingError).to.be.false();
-            });
-
-            it('should return true if there is a rounding error of 0.11%', async () => {
-                const numerator = new BigNumber(20);
-                const denominator = new BigNumber(9989);
-                const target = new BigNumber(500);
-                // rounding error = ((20*500/9989) - floor(20*500/9989)) / (20*500/9989) = 0.011%
-                const isRoundingError = await libs.publicIsRoundingError.callAsync(numerator, denominator, target);
-                expect(isRoundingError).to.be.true();
-            });
-
-            it('should return true if there is a rounding error > 0.1%', async () => {
-                const numerator = new BigNumber(3);
-                const denominator = new BigNumber(7);
-                const target = new BigNumber(10);
-                // rounding error = ((3*10/7) - floor(3*10/7)) / (3*10/7) = 6.67%
-                const isRoundingError = await libs.publicIsRoundingError.callAsync(numerator, denominator, target);
-                expect(isRoundingError).to.be.true();
-            });
-
-            it('should return false when there is no rounding error', async () => {
-                const numerator = new BigNumber(1);
-                const denominator = new BigNumber(2);
-                const target = new BigNumber(10);
-
-                const isRoundingError = await libs.publicIsRoundingError.callAsync(numerator, denominator, target);
-                expect(isRoundingError).to.be.false();
-            });
-
-            it('should return false when there is rounding error <= 0.1%', async () => {
-                // randomly generated numbers
-                const numerator = new BigNumber(76564);
-                const denominator = new BigNumber(676373677);
-                const target = new BigNumber(105762562);
-                // rounding error = ((76564*105762562/676373677) - floor(76564*105762562/676373677)) /
-                // (76564*105762562/676373677) = 0.0007%
-                const isRoundingError = await libs.publicIsRoundingError.callAsync(numerator, denominator, target);
-                expect(isRoundingError).to.be.false();
-            });
-        });
-
-        describe('getPartialAmount', () => {
-            it('should return the numerator/denominator*target', async () => {
-                const numerator = new BigNumber(1);
-                const denominator = new BigNumber(2);
-                const target = new BigNumber(10);
-
-                const partialAmount = await libs.publicGetPartialAmount.callAsync(numerator, denominator, target);
-                const expectedPartialAmount = 5;
-                expect(partialAmount).to.be.bignumber.equal(expectedPartialAmount);
-            });
-
-            it('should round down', async () => {
-                const numerator = new BigNumber(2);
-                const denominator = new BigNumber(3);
-                const target = new BigNumber(10);
-
-                const partialAmount = await libs.publicGetPartialAmount.callAsync(numerator, denominator, target);
-                const expectedPartialAmount = 6;
-                expect(partialAmount).to.be.bignumber.equal(expectedPartialAmount);
-            });
-
-            it('should round .5 down', async () => {
-                const numerator = new BigNumber(1);
-                const denominator = new BigNumber(20);
-                const target = new BigNumber(10);
-
-                const partialAmount = await libs.publicGetPartialAmount.callAsync(numerator, denominator, target);
-                const expectedPartialAmount = 0;
-                expect(partialAmount).to.be.bignumber.equal(expectedPartialAmount);
-            });
-        });
-    });
 });
diff --git a/packages/contracts/test/utils/artifacts.ts b/packages/contracts/test/utils/artifacts.ts
index 63bd555a4..e608ee174 100644
--- a/packages/contracts/test/utils/artifacts.ts
+++ b/packages/contracts/test/utils/artifacts.ts
@@ -16,6 +16,7 @@ import * as MultiSigWalletWithTimeLock from '../../artifacts/MultiSigWalletWithT
 import * as TestAssetProxyDispatcher from '../../artifacts/TestAssetProxyDispatcher.json';
 import * as TestAssetProxyOwner from '../../artifacts/TestAssetProxyOwner.json';
 import * as TestConstants from '../../artifacts/TestConstants.json';
+import * as TestExchangeInternals from '../../artifacts/TestExchangeInternals.json';
 import * as TestLibBytes from '../../artifacts/TestLibBytes.json';
 import * as TestLibs from '../../artifacts/TestLibs.json';
 import * as TestSignatureValidator from '../../artifacts/TestSignatureValidator.json';
@@ -46,6 +47,7 @@ export const artifacts = {
     TestConstants: (TestConstants as any) as ContractArtifact,
     TestLibBytes: (TestLibBytes as any) as ContractArtifact,
     TestLibs: (TestLibs as any) as ContractArtifact,
+    TestExchangeInternals: (TestExchangeInternals as any) as ContractArtifact,
     TestSignatureValidator: (TestSignatureValidator as any) as ContractArtifact,
     Validator: (Validator as any) as ContractArtifact,
     Wallet: (Wallet as any) as ContractArtifact,
diff --git a/packages/contracts/test/utils/assertions.ts b/packages/contracts/test/utils/assertions.ts
index 112a470f6..61df800c8 100644
--- a/packages/contracts/test/utils/assertions.ts
+++ b/packages/contracts/test/utils/assertions.ts
@@ -15,6 +15,14 @@ let nodeType: NodeType | undefined;
 // resolve with either a transaction receipt or a transaction hash.
 export type sendTransactionResult = Promise<TransactionReceipt | TransactionReceiptWithDecodedLogs | string>;
 
+/**
+ * Returns ganacheError if the backing Ethereum node is Ganache and gethError
+ * if it is Geth.
+ * @param ganacheError the error to be returned if the backing node is Ganache.
+ * @param gethError the error to be returned if the backing node is Geth.
+ * @returns either the given ganacheError or gethError depending on the backing
+ * node.
+ */
 async function _getGanacheOrGethError(ganacheError: string, gethError: string): Promise<string> {
     if (_.isUndefined(nodeType)) {
         nodeType = await web3Wrapper.getNodeTypeAsync();
@@ -42,6 +50,25 @@ async function _getContractCallFailedErrorMessageAsync(): Promise<string> {
 }
 
 /**
+ * Returns the expected error message for an 'invalid opcode' resulting from a
+ * contract call. The exact error message depends on the backing Ethereum node.
+ */
+export async function getInvalidOpcodeErrorMessageForCallAsync(): Promise<string> {
+    return _getGanacheOrGethError('invalid opcode', 'Contract call failed');
+}
+
+/**
+ * Returns the expected error message for the given revert reason resulting from
+ * a sendTransaction call. The exact error message depends on the backing
+ * Ethereum node and whether it supports revert reasons.
+ * @param reason a specific revert reason.
+ * @returns the expected error message.
+ */
+export async function getRevertReasonOrErrorMessageForSendTransactionAsync(reason: RevertReason): Promise<string> {
+    return _getGanacheOrGethError(reason, 'always failing transaction');
+}
+
+/**
  * Rejects if the given Promise does not reject with an error indicating
  * insufficient funds.
  * @param p a promise resulting from a contract call or sendTransaction call.
diff --git a/packages/contracts/test/utils/combinatorial_utils.ts b/packages/contracts/test/utils/combinatorial_utils.ts
new file mode 100644
index 000000000..d72b41f8a
--- /dev/null
+++ b/packages/contracts/test/utils/combinatorial_utils.ts
@@ -0,0 +1,113 @@
+import { BigNumber } from '@0xproject/utils';
+import * as combinatorics from 'js-combinatorics';
+
+import { testWithReferenceFuncAsync } from './test_with_reference';
+
+// A set of values corresponding to the uint256 type in Solidity. This set
+// contains some notable edge cases, including some values which will overflow
+// the uint256 type when used in different mathematical operations.
+export const uint256Values = [
+    new BigNumber(0),
+    new BigNumber(1),
+    new BigNumber(2),
+    // Non-trivial big number.
+    new BigNumber(2).pow(64),
+    // Max that does not overflow when squared.
+    new BigNumber(2).pow(128).minus(1),
+    // Min that does overflow when squared.
+    new BigNumber(2).pow(128),
+    // Max that does not overflow when doubled.
+    new BigNumber(2).pow(255).minus(1),
+    // Min that does overflow when doubled.
+    new BigNumber(2).pow(255),
+    // Max that does not overflow.
+    new BigNumber(2).pow(256).minus(1),
+];
+
+// A set of values corresponding to the bytes32 type in Solidity.
+export const bytes32Values = [
+    // Min
+    '0x0000000000000000000000000000000000000000000000000000000000000000',
+    '0x0000000000000000000000000000000000000000000000000000000000000001',
+    '0x0000000000000000000000000000000000000000000000000000000000000002',
+    // Non-trivial big number.
+    '0x000000000000f000000000000000000000000000000000000000000000000000',
+    // Max
+    '0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff',
+];
+
+export async function testCombinatoriallyWithReferenceFuncAsync<P0, P1, R>(
+    name: string,
+    referenceFunc: (p0: P0, p1: P1) => Promise<R>,
+    testFunc: (p0: P0, p1: P1) => Promise<R>,
+    allValues: [P0[], P1[]],
+): Promise<void>;
+export async function testCombinatoriallyWithReferenceFuncAsync<P0, P1, P2, R>(
+    name: string,
+    referenceFunc: (p0: P0, p1: P1, p2: P2) => Promise<R>,
+    testFunc: (p0: P0, p1: P1, p2: P2) => Promise<R>,
+    allValues: [P0[], P1[], P2[]],
+): Promise<void>;
+export async function testCombinatoriallyWithReferenceFuncAsync<P0, P1, P2, P3, R>(
+    name: string,
+    referenceFunc: (p0: P0, p1: P1, p2: P2, p3: P3) => Promise<R>,
+    testFunc: (p0: P0, p1: P1, p2: P2, p3: P3) => Promise<R>,
+    allValues: [P0[], P1[], P2[], P3[]],
+): Promise<void>;
+export async function testCombinatoriallyWithReferenceFuncAsync<P0, P1, P2, P3, P4, R>(
+    name: string,
+    referenceFunc: (p0: P0, p1: P1, p2: P2, p3: P3, p4: P4) => Promise<R>,
+    testFunc: (p0: P0, p1: P1, p2: P2, p3: P3, p4: P4) => Promise<R>,
+    allValues: [P0[], P1[], P2[], P3[], P4[]],
+): Promise<void>;
+
+/**
+ * Uses combinatorics to test the behavior of a test function by comparing it to
+ * the expected behavior (defined by a reference function) for a large number of
+ * possible input values.
+ *
+ * First generates test cases by taking the cartesian product of the given
+ * values. Each test case is a set of N values corresponding to the N arguments
+ * for the test func and the reference func. For each test case, first the
+ * reference function will be called to obtain an "expected result", or if the
+ * reference function throws/rejects, an "expected error". Next, the test
+ * function will be called to obtain an "actual result", or if the test function
+ * throws/rejects, an "actual error". Each test case passes if at least one of
+ * the following conditions is met:
+ *
+ * 1) Neither the reference function or the test function throw and the
+ * "expected result" equals the "actual result".
+ *
+ * 2) Both the reference function and the test function throw and the "actual
+ * error" message *contains* the "expected error" message.
+ *
+ * The first test case which does not meet one of these conditions will cause
+ * the entire test to fail and this function will throw/reject.
+ *
+ * @param referenceFuncAsync a reference function implemented in pure
+ * JavaScript/TypeScript which accepts N arguments and returns the "expected
+ * result" or "expected error" for a given test case.
+ * @param testFuncAsync a test function which, e.g., makes a call or sends a
+ * transaction to a contract. It accepts the same N arguments returns the
+ * "actual result" or "actual error" for a given test case.
+ * @param values an array of N arrays. Each inner array is a set of possible
+ * values which are passed into both the reference function and the test
+ * function.
+ * @return A Promise that resolves if the test passes and rejects if the test
+ * fails, according to the rules described above.
+ */
+export async function testCombinatoriallyWithReferenceFuncAsync(
+    name: string,
+    referenceFuncAsync: (...args: any[]) => Promise<any>,
+    testFuncAsync: (...args: any[]) => Promise<any>,
+    allValues: any[],
+): Promise<void> {
+    const testCases = combinatorics.cartesianProduct(...allValues);
+    let counter = 0;
+    testCases.forEach(async testCase => {
+        counter += 1;
+        it(`${name} ${counter}/${testCases.length}`, async () => {
+            await testWithReferenceFuncAsync(referenceFuncAsync, testFuncAsync, testCase as any);
+        });
+    });
+}
diff --git a/packages/contracts/test/utils/core_combinatorial_utils.ts b/packages/contracts/test/utils/fill_order_combinatorial_utils.ts
index 44a5199c0..bdd1e62a2 100644
--- a/packages/contracts/test/utils/core_combinatorial_utils.ts
+++ b/packages/contracts/test/utils/fill_order_combinatorial_utils.ts
@@ -46,16 +46,16 @@ chaiSetup.configure();
 const expect = chai.expect;
 
 /**
- * Instantiates a new instance of CoreCombinatorialUtils. Since this method has some
+ * Instantiates a new instance of FillOrderCombinatorialUtils. Since this method has some
  * required async setup, a factory method is required.
  * @param web3Wrapper Web3Wrapper instance
  * @param txDefaults Default Ethereum tx options
- * @return CoreCombinatorialUtils instance
+ * @return FillOrderCombinatorialUtils instance
  */
-export async function coreCombinatorialUtilsFactoryAsync(
+export async function fillOrderCombinatorialUtilsFactoryAsync(
     web3Wrapper: Web3Wrapper,
     txDefaults: Partial<TxData>,
-): Promise<CoreCombinatorialUtils> {
+): Promise<FillOrderCombinatorialUtils> {
     const accounts = await web3Wrapper.getAvailableAddressesAsync();
     const userAddresses = _.slice(accounts, 0, 5);
     const [ownerAddress, makerAddress, takerAddress] = userAddresses;
@@ -123,7 +123,7 @@ export async function coreCombinatorialUtilsFactoryAsync(
         exchangeContract.address,
     );
 
-    const coreCombinatorialUtils = new CoreCombinatorialUtils(
+    const fillOrderCombinatorialUtils = new FillOrderCombinatorialUtils(
         orderFactory,
         ownerAddress,
         makerAddress,
@@ -133,10 +133,10 @@ export async function coreCombinatorialUtilsFactoryAsync(
         exchangeWrapper,
         assetWrapper,
     );
-    return coreCombinatorialUtils;
+    return fillOrderCombinatorialUtils;
 }
 
-export class CoreCombinatorialUtils {
+export class FillOrderCombinatorialUtils {
     public orderFactory: OrderFactoryFromScenario;
     public ownerAddress: string;
     public makerAddress: string;
@@ -240,7 +240,7 @@ export class CoreCombinatorialUtils {
             // AllowanceAmountScenario.TooLow,
             // AllowanceAmountScenario.Unlimited,
         ];
-        const fillScenarioArrays = CoreCombinatorialUtils._getAllCombinations([
+        const fillScenarioArrays = FillOrderCombinatorialUtils._getAllCombinations([
             takerScenarios,
             feeRecipientScenarios,
             makerAssetAmountScenario,
@@ -309,7 +309,7 @@ export class CoreCombinatorialUtils {
         } else {
             const result = [];
             const restOfArrays = arrays.slice(1);
-            const allCombinationsOfRemaining = CoreCombinatorialUtils._getAllCombinations(restOfArrays); // recur with the rest of array
+            const allCombinationsOfRemaining = FillOrderCombinatorialUtils._getAllCombinations(restOfArrays); // recur with the rest of array
             // tslint:disable:prefer-for-of
             for (let i = 0; i < allCombinationsOfRemaining.length; i++) {
                 for (let j = 0; j < arrays[0].length; j++) {
diff --git a/packages/contracts/test/utils/test_with_reference.ts b/packages/contracts/test/utils/test_with_reference.ts
new file mode 100644
index 000000000..599b1eed4
--- /dev/null
+++ b/packages/contracts/test/utils/test_with_reference.ts
@@ -0,0 +1,119 @@
+import * as chai from 'chai';
+import * as _ from 'lodash';
+
+import { chaiSetup } from './chai_setup';
+
+chaiSetup.configure();
+const expect = chai.expect;
+
+export async function testWithReferenceFuncAsync<P0, R>(
+    referenceFunc: (p0: P0) => Promise<R>,
+    testFunc: (p0: P0) => Promise<R>,
+    values: [P0],
+): Promise<void>;
+export async function testWithReferenceFuncAsync<P0, P1, R>(
+    referenceFunc: (p0: P0, p1: P1) => Promise<R>,
+    testFunc: (p0: P0, p1: P1) => Promise<R>,
+    values: [P0, P1],
+): Promise<void>;
+export async function testWithReferenceFuncAsync<P0, P1, P2, R>(
+    referenceFunc: (p0: P0, p1: P1, p2: P2) => Promise<R>,
+    testFunc: (p0: P0, p1: P1, p2: P2) => Promise<R>,
+    values: [P0, P1, P2],
+): Promise<void>;
+export async function testWithReferenceFuncAsync<P0, P1, P2, P3, R>(
+    referenceFunc: (p0: P0, p1: P1, p2: P2, p3: P3) => Promise<R>,
+    testFunc: (p0: P0, p1: P1, p2: P2, p3: P3) => Promise<R>,
+    values: [P0, P1, P2, P3],
+): Promise<void>;
+export async function testWithReferenceFuncAsync<P0, P1, P2, P3, P4, R>(
+    referenceFunc: (p0: P0, p1: P1, p2: P2, p3: P3, p4: P4) => Promise<R>,
+    testFunc: (p0: P0, p1: P1, p2: P2, p3: P3, p4: P4) => Promise<R>,
+    values: [P0, P1, P2, P3, P4],
+): Promise<void>;
+
+/**
+ * Tests the behavior of a test function by comparing it to the expected
+ * behavior (defined by a reference function).
+ *
+ * First the reference function will be called to obtain an "expected result",
+ * or if the reference function throws/rejects, an "expected error". Next, the
+ * test function will be called to obtain an "actual result", or if the test
+ * function throws/rejects, an "actual error". The test passes if at least one
+ * of the following conditions is met:
+ *
+ * 1) Neither the reference function or the test function throw and the
+ * "expected result" equals the "actual result".
+ *
+ * 2) Both the reference function and the test function throw and the "actual
+ * error" message *contains* the "expected error" message.
+ *
+ * @param referenceFuncAsync a reference function implemented in pure
+ * JavaScript/TypeScript which accepts N arguments and returns the "expected
+ * result" or throws/rejects with the "expected error".
+ * @param testFuncAsync a test function which, e.g., makes a call or sends a
+ * transaction to a contract. It accepts the same N arguments returns the
+ * "actual result" or throws/rejects with the "actual error".
+ * @param values an array of N values, where each value corresponds in-order to
+ * an argument to both the test function and the reference function.
+ * @return A Promise that resolves if the test passes and rejects if the test
+ * fails, according to the rules described above.
+ */
+export async function testWithReferenceFuncAsync(
+    referenceFuncAsync: (...args: any[]) => Promise<any>,
+    testFuncAsync: (...args: any[]) => Promise<any>,
+    values: any[],
+): Promise<void> {
+    let expectedResult: any;
+    let expectedErr: string | undefined;
+    try {
+        expectedResult = await referenceFuncAsync(...values);
+    } catch (e) {
+        expectedErr = e.message;
+    }
+    let actualResult: any | undefined;
+    try {
+        actualResult = await testFuncAsync(...values);
+        if (!_.isUndefined(expectedErr)) {
+            throw new Error(
+                `Expected error containing ${expectedErr} but got no error\n\tTest case: ${_getTestCaseString(
+                    referenceFuncAsync,
+                    values,
+                )}`,
+            );
+        }
+    } catch (e) {
+        if (_.isUndefined(expectedErr)) {
+            throw new Error(`${e.message}\n\tTest case: ${_getTestCaseString(referenceFuncAsync, values)}`);
+        } else {
+            expect(e.message).to.contain(
+                expectedErr,
+                `${e.message}\n\tTest case: ${_getTestCaseString(referenceFuncAsync, values)}`,
+            );
+        }
+    }
+    if (!_.isUndefined(actualResult) && !_.isUndefined(expectedResult)) {
+        expect(actualResult).to.deep.equal(
+            expectedResult,
+            `Test case: ${_getTestCaseString(referenceFuncAsync, values)}`,
+        );
+    }
+}
+
+function _getTestCaseString(referenceFuncAsync: (...args: any[]) => Promise<any>, values: any[]): string {
+    const paramNames = _getParameterNames(referenceFuncAsync);
+    return JSON.stringify(_.zipObject(paramNames, values));
+}
+
+// Source: https://stackoverflow.com/questions/1007981/how-to-get-function-parameter-names-values-dynamically
+function _getParameterNames(func: (...args: any[]) => any): string[] {
+    return _.toString(func)
+        .replace(/[/][/].*$/gm, '') // strip single-line comments
+        .replace(/\s+/g, '') // strip white space
+        .replace(/[/][*][^/*]*[*][/]/g, '') // strip multi-line comments
+        .split('){', 1)[0]
+        .replace(/^[^(]*[(]/, '') // extract the parameters
+        .replace(/=[^,]+/g, '') // strip any ES6 defaults
+        .split(',')
+        .filter(Boolean); // split & filter [""]
+}