fix improper warnings for invalid reporters (#4275)

* fix improper warnings for invalid reporters

    also: reorganize, add, and refactor a bunch of problematic unit tests for `lib/mocha.js`.  better isolation except where we can't really do that (calling `require`)

    there's still missing tests in here, but this is an improvement.

* restrict use of Object.assign in ESLint config
* add wrapper around process.cwd()
    - better isolation
    - a use of `process.cwd()` in `lib/runner.js` was left in place to avoid conflicts, because another PR will remove it

.eslintrc.yml

@@ -14,6 +14,11 @@ rules:
   strict:
     - error
     - safe
+  # disallow Object.assign
+  no-restricted-properties:
+    - error
+    - object: 'Object'
+      property: 'assign'
 overrides:
   - files:
       - scripts/**/*.js
@@ -31,6 +36,11 @@ overrides:
       ecmaVersion: 2018
     env:
       browser: false
+    rules:
+      no-restricted-properties:
+        - off
+        - object: 'Object'
+          property: 'assign'
   - files:
       - esm-utils.js
     parserOptions:
@@ -79,7 +89,6 @@ overrides:
         # disallow property access of `global.<timer>.*`
         - selector: '*[object.object.name=global][object.property.name=/(Date|(set|clear)(Timeout|Immediate|Interval))/]:expression'
           message: *GH-237
-
   - files:
       - test/**/*.mjs
     parserOptions:

lib/cli/cli.js

@@ -19,6 +19,7 @@ const {loadOptions, YARGS_PARSER_CONFIG} = require('./options');
 const commands = require('./commands');
 const ansi = require('ansi-colors');
 const {repository, homepage, version, gitter} = require('../../package.json');
+const {cwd} = require('../utils');
 
 /**
  * - Accepts an `Array` of arguments
@@ -31,7 +32,7 @@ exports.main = (argv = process.argv.slice(2)) => {
   debug('entered main with raw args', argv);
   // ensure we can require() from current working directory
   if (typeof module.paths !== 'undefined') {
-    module.paths.push(process.cwd(), path.resolve('node_modules'));
+    module.paths.push(cwd(), path.resolve('node_modules'));
   }
 
   Error.stackTraceLimit = Infinity; // configurable via --stack-trace-limit?

lib/cli/config.js

@@ -11,6 +11,7 @@ const fs = require('fs');
 const path = require('path');
 const debug = require('debug')('mocha:cli:config');
 const findUp = require('find-up');
+const utils = require('../utils');
 
 /**
  * These are the valid config files, in order of precedence;
@@ -92,7 +93,7 @@ exports.loadConfig = filepath => {
  * @param {string} [cwd] - Current working directory
  * @returns {string|null} Filepath to config, if found
  */
-exports.findConfig = (cwd = process.cwd()) => {
+exports.findConfig = (cwd = utils.cwd()) => {
   const filepath = findUp.sync(exports.CONFIG_FILES, {cwd});
   if (filepath) {
     debug('findConfig: found config file %s', filepath);

lib/mocha.js

@@ -58,7 +58,7 @@ var mochaStates = utils.defineConstants({
  */
 
 if (!process.browser && typeof module.paths !== 'undefined') {
-  var cwd = process.cwd();
+  var cwd = utils.cwd();
   module.paths.push(cwd, path.join(cwd, 'node_modules'));
 }
 
@@ -231,24 +231,24 @@ Mocha.prototype.reporter = function(reporter, reporterOptions) {
         _reporter = require(reporter);
       } catch (err) {
         if (
-          err.code !== 'MODULE_NOT_FOUND' ||
-          err.message.indexOf('Cannot find module') !== -1
+          err.code === 'MODULE_NOT_FOUND' ||
+          err.message.indexOf('Cannot find module') >= 0
         ) {
           // Try to load reporters from a path (absolute or relative)
           try {
-            _reporter = require(path.resolve(process.cwd(), reporter));
+            _reporter = require(path.resolve(utils.cwd(), reporter));
           } catch (_err) {
-            _err.code !== 'MODULE_NOT_FOUND' ||
-            _err.message.indexOf('Cannot find module') !== -1
-              ? console.warn(sQuote(reporter) + ' reporter not found')
-              : console.warn(
+            _err.code === 'MODULE_NOT_FOUND' ||
+            _err.message.indexOf('Cannot find module') >= 0
+              ? utils.warn(sQuote(reporter) + ' reporter not found')
+              : utils.warn(
                   sQuote(reporter) +
                     ' reporter blew up with error:\n' +
                     err.stack
                 );
           }
         } else {
-          console.warn(
+          utils.warn(
             sQuote(reporter) + ' reporter blew up with error:\n' + err.stack
           );
         }

lib/utils.js

@@ -637,7 +637,7 @@ exports.stackTraceFilter = function() {
   var slash = path.sep;
   var cwd;
   if (is.node) {
-    cwd = process.cwd() + slash;
+    cwd = exports.cwd() + slash;
   } else {
     cwd = (typeof location === 'undefined'
       ? window.location
@@ -821,3 +821,13 @@ exports.supportsEsModules = function() {
     }
   }
 };
+
+/**
+ * Returns current working directory
+ *
+ * Wrapper around `process.cwd()` for isolation
+ * @private
+ */
+exports.cwd = function cwd() {
+  return process.cwd();
+};