Exchange signature validation fuzz tests (#2425)

* `@0x/contracts-integrations`: Add Exchange signature validation fuzz tests.

* `@0x/contracts-integrations`: Switch from actor pattern to just pure function generators.

Co-authored-by: Lawrence Forman <me@merklejerk.com>

contracts/integrations/test/framework/deployment_manager.ts

@@ -22,6 +22,7 @@ import {
 } from '@0x/contracts-staking';
 import { BlockchainTestsEnvironment, constants } from '@0x/contracts-test-utils';
 import { BigNumber } from '@0x/utils';
+import { Web3Wrapper } from '@0x/web3-wrapper';
 import { TxData } from 'ethereum-types';
 import * as _ from 'lodash';
 
@@ -207,6 +208,7 @@ export class DeploymentManager {
 
         // Construct the new instance and return it.
         return new DeploymentManager(
+            environment.web3Wrapper,
             assetProxies,
             governor,
             exchange,
@@ -522,6 +524,7 @@ export class DeploymentManager {
     }
 
     protected constructor(
+        public web3Wrapper: Web3Wrapper,
         public assetProxies: AssetProxyContracts,
         public governor: ZeroExGovernorContract,
         public exchange: ExchangeContract,

contracts/integrations/test/framework/simulation.ts

@@ -48,6 +48,7 @@ export class SimulationEnvironment {
 
 export abstract class Simulation {
     public readonly generator = this._assertionGenerator();
+    public resets = false;
 
     constructor(public environment: SimulationEnvironment) {}
 
@@ -66,11 +67,15 @@ export abstract class Simulation {
     protected abstract _assertionGenerator(): AsyncIterableIterator<AssertionResult | void>;
 
     private async _stepAsync(): Promise<void> {
+        const snapshotId = this.resets ? await this.environment.deployment.web3Wrapper.takeSnapshotAsync() : undefined;
         try {
             await this.generator.next();
         } catch (error) {
             logger.logFailure(error, this.environment.state());
             throw error;
         }
+        if (snapshotId !== undefined) {
+            await this.environment.deployment.web3Wrapper.revertSnapshotAsync(snapshotId);
+        }
     }
 }

contracts/integrations/test/framework/utils/pseudorandom.ts

@@ -78,6 +78,17 @@ class PRNGWrapper {
             return ONE.minus(ONE.minus(u).exponentiatedBy(ONE.dividedBy(beta))).exponentiatedBy(ONE.dividedBy(alpha));
         };
     }
+
+    /*
+     * Pseudorandom version of `hexRandom()`. If no distribution is provided,
+     * samples all byte values uniformly.
+     */
+    public hex(bytesLength: number = 32, distribution: () => Numberish = this.rng): string {
+        const buf = Buffer.from(_.times(bytesLength, () => this.integer(0, 255, distribution).toNumber())).toString(
+            'hex',
+        );
+        return `0x${buf}`;
+    }
 }
 
 export const Pseudorandom = new PRNGWrapper();