make chai a dependency

package.json

@@ -37,6 +37,7 @@
   "dependencies": {
     "@truffle/contract": "^4.0.35",
     "ansi-colors": "^3.2.3",
+    "chai": "^4.2.0",
     "chai-bn": "^0.2.0",
     "ethjs-abi": "^0.2.1",
     "lodash.flatten": "^4.4.0",
@@ -46,7 +47,6 @@
   },
   "devDependencies": {
     "@openzeppelin/contract-loader": "^0.1.0",
-    "chai": "^4.2.0",
     "eslint": "^5.9.0",
     "eslint-config-standard": "^12.0.0",
     "eslint-plugin-import": "^2.14.0",
@@ -56,8 +56,5 @@
     "eslint-plugin-standard": "^4.0.0",
     "ganache-cli": "^6.5.0",
     "truffle": "^5.0.29"
-  },
-  "peerDependencies": {
-    "chai": "^4.2.0"
   }
 }

src/setup.js

@@ -2,10 +2,20 @@ require('../configure')();
 
 const web3 = require('./config/web3').getWeb3();
 
-const chai = require('chai');
 const BN = web3.utils.BN;
+const chaiBN = require('chai-bn')(BN);
 
-chai.use(require('chai-bn')(BN));
+require('chai').use(chaiBN);
+
+// Installing chai-bn for the user is part of the offering.
+//
+// The chai module used internally by us may not be the same one that the user
+// has in their own tests. This can happen if the version ranges required don't
+// intersect, or if the package manager doesn't dedupe the modules for any
+// other reason. We do our best to install chai-bn for the user.
+function useChaiBN (chai) { if (chai) chai.use(chaiBN); }
+useChaiBN(require.main.require('chai'));
+useChaiBN(module.parent.require('chai'));
 
 module.exports = {
   web3,

test-integration/chai-bn/package.json

@@ -0,0 +1,14 @@
+{
+  "name": "chai-bn",
+  "version": "1.0.0",
+  "private": true,
+  "scripts": {
+    "test": "node test.js"
+  },
+  "author": "Francisco Giordano <[email protected]>",
+  "license": "MIT",
+  "dependencies": {
+    "chai": "^3.5.0",
+    "semver": "^6.3.0"
+  }
+}

test-integration/chai-bn/run.sh

@@ -0,0 +1,17 @@
+#!/bin/bash
+
+set -o errexit
+
+cd "$(dirname $0)"
+
+# Get a package like a user would install
+pkg="$(npm pack ../../ 2> /dev/null)"
+
+# Clean it up afterwards
+trap "rm -f $pkg" EXIT
+
+npm install
+
+npm install --no-save "$pkg"
+
+npm test

test-integration/chai-bn/test.js

@@ -0,0 +1,23 @@
+// Validate that this is testing what we want: that this package uses a
+// different chai module than the one being used internally by test-helpers.
+// This is verified by checking that the chai versions don't intersect, so that
+// the package manager is unable to dedupe them.
+const assert = require('assert');
+const semver = require('semver');
+
+const our = require('./package.json');
+const testHelpers = require('@openzeppelin/test-helpers/package.json');
+
+assert(
+  !semver.intersects(our.dependencies.chai, testHelpers.dependencies.chai),
+  'Integration test is not set up correctly: chai module may be deduped',
+);
+
+// Even though we're using different chai modules, chai-bn is still being
+// installed.
+require('@openzeppelin/test-helpers');
+
+const { expect } = require('chai');
+
+// If chai-bn is not installed the following line will fail.
+expect('1').to.bignumber.equal('1');