assert mocha is bundle-able by webpack; fixes mochajs#4422

lib/mocha.js

@@ -12,18 +12,18 @@ var builtinReporters = require('./reporters');
 var growl = require('./nodejs/growl');
 var utils = require('./utils');
 var mocharc = require('./mocharc.json');
-var errors = require('./errors');
 var Suite = require('./suite');
 var esmUtils = utils.supportsEsModules(true)
   ? require('./esm-utils')
   : undefined;
 var createStatsCollector = require('./stats-collector');
-var createInvalidReporterError = errors.createInvalidReporterError;
-var createInvalidInterfaceError = errors.createInvalidInterfaceError;
-var createMochaInstanceAlreadyDisposedError =
-  errors.createMochaInstanceAlreadyDisposedError;
-var createMochaInstanceAlreadyRunningError =
-  errors.createMochaInstanceAlreadyRunningError;
+const {
+  createUnsupportedError,
+  createInvalidInterfaceError,
+  createInvalidReporterError,
+  createMochaInstanceAlreadyDisposedError,
+  createMochaInstanceAlreadyRunningError
+} = require('./errors');
 var EVENT_FILE_PRE_REQUIRE = Suite.constants.EVENT_FILE_PRE_REQUIRE;
 var EVENT_FILE_POST_REQUIRE = Suite.constants.EVENT_FILE_POST_REQUIRE;
 var EVENT_FILE_REQUIRE = Suite.constants.EVENT_FILE_REQUIRE;
@@ -445,7 +445,12 @@ Mocha.prototype.loadFilesAsync = function() {
  * @param {string} file - Pathname of file to be unloaded.
  */
 Mocha.unloadFile = function(file) {
-  delete require.cache[require.resolve(file)];
+  if (utils.isBrowser()) {
+    throw createUnsupportedError(
+      'unloadFile() is only suported in a Node.js environment'
+    );
+  }
+  return require('./nodejs/file-unloader').unloadFile(file);
 };
 
 /**
@@ -1051,9 +1056,7 @@ Mocha.prototype.rootHooks = function rootHooks(hooks) {
  */
 Mocha.prototype.parallelMode = function parallelMode(enable) {
   if (utils.isBrowser()) {
-    throw errors.createUnsupportedError(
-      'parallel mode is only supported in Node.js'
-    );
+    throw createUnsupportedError('parallel mode is only supported in Node.js');
   }
   var parallel = enable === true;
   if (
@@ -1064,7 +1067,7 @@ Mocha.prototype.parallelMode = function parallelMode(enable) {
     return this;
   }
   if (this._state !== mochaStates.INIT) {
-    throw errors.createUnsupportedError(
+    throw createUnsupportedError(
       'cannot change parallel mode after having called run()'
     );
   }

lib/nodejs/file-unloader.js

@@ -0,0 +1,15 @@
+'use strict';
+
+/**
+ * This module should not be in the browser bundle, so it's here.
+ * @private
+ * @module
+ */
+
+/**
+ * Deletes a file from the `require` cache.
+ * @param {string} file - File
+ */
+exports.unloadFile = file => {
+  delete require.cache[require.resolve(file)];
+};