feat(mocha): allow plugin to pick up .mocharc files

We want to delegate as much configuration to tools themselves rather
than exposing options via Tool Kit. Unfortunately, the mocha plugin was
invoking mocha with a low-level API and skipping the code which reads
configuration files, meaning that users could not set options like they
can with plugins such as Jest and Webpack.

To solve this let's just invoke the mocha CLI directly rather than via a
lower-level API so that it calls all the setup code it would for a
normal invocation, including looking for configuration files. The user
can also set the path for the config file explicitly in the Tool Kit
options.

The files that mocha reads can now be set in its own configuration file
so we don't really need to have them be set by Tool Kit. The option to
do so might be removed in a future major release of the plugin.

lib/types/src/schema/mocha.ts

@@ -1,7 +1,8 @@
 import { SchemaOutput } from '../schema'
 
 export const MochaSchema = {
-  files: 'string'
+  files: 'string',
+  configPath: 'string?'
 } as const
 export type MochaOptions = SchemaOutput<typeof MochaSchema>
 

plugins/mocha/src/tasks/mocha.ts

@@ -1,9 +1,9 @@
-import { hookConsole, styles } from '@dotcom-tool-kit/logger'
+import { hookFork, waitOnExit } from '@dotcom-tool-kit/logger'
 import { Task } from '@dotcom-tool-kit/types'
-import MochaCore from 'mocha'
 import { glob } from 'glob'
-import { ToolKitError } from '@dotcom-tool-kit/error'
 import { MochaOptions, MochaSchema } from '@dotcom-tool-kit/types/lib/schema/mocha'
+import { fork } from 'child_process'
+const mochaCLIPath = require.resolve('mocha/bin/mocha')
 
 export default class Mocha extends Task<typeof MochaSchema> {
   static description = ''
@@ -13,34 +13,12 @@ export default class Mocha extends Task<typeof MochaSchema> {
   }
 
   async run(): Promise<void> {
-    const mocha = new MochaCore()
-
     const files = glob.sync(this.options.files)
-    if (files.length === 0) {
-      const error = new ToolKitError('No test files found')
-      error.details = `We looked for files matching ${styles.filepath(
-        this.options.files
-      )}, but there weren't any. Set ${styles.title(
-        'options."@dotcom-tool-kit/mocha".files'
-      )} in your Tool Kit configuration to change this file pattern.`
-      throw error
-    }
-
-    files.forEach((file) => {
-      mocha.addFile(file)
-    })
 
-    const unhook = hookConsole(this.logger, 'mocha')
-    await new Promise<void>((resolve, reject) => {
-      mocha.run((failures) => {
-        if (failures > 0) {
-          const error = new ToolKitError('mocha tests failed')
-          error.details = 'please fix the test failures and retry'
-          reject(error)
-        } else {
-          resolve()
-        }
-      })
-    }).finally(() => unhook())
+    const args = [this.options.configPath ? `--config=${this.options.configPath}` : '', ...files]
+    this.logger.info(`running mocha ${args.join(' ')}`)
+    const child = fork(mochaCLIPath, args, { silent: true })
+    hookFork(this.logger, 'mocha', child)
+    return waitOnExit('mocha', child)
   }
 }