feat(ui): mocha task

packages/@vue/cli-plugin-unit-mocha/ui.js

@@ -0,0 +1,18 @@
+module.exports = api => {
+  api.describeTask({
+    match: /vue-cli-service test:unit/,
+    description: 'mocha.tasks.test.description',
+    link: 'https://github.com/vuejs/vue-cli/tree/dev/packages/%40vue/cli-plugin-unit-mocha#injected-commands',
+    prompts: [
+      {
+        name: 'watch',
+        type: 'confirm',
+        default: false,
+        description: 'mocha.tasks.test.watch'
+      }
+    ],
+    onBeforeRun: ({ answers, args }) => {
+      if (answers.watch) args.push('--watch')
+    }
+  })
+}

packages/@vue/cli-ui/locales/en.json

@@ -543,5 +543,13 @@
         "update": "Re-record every snapshot that fails during this test run"
       }
     }
+  },
+  "mocha": {
+    "tasks": {
+      "test": {
+        "description": "Run unit tests with Mocha",
+        "watch": "Watch files for changes and rerun tests related to changed files"
+      }
+    }
   }
 }