chore(mp): add usingComponents tests (#3035)

packages/uni-cli-shared/__tests__/jsFile.spec.ts

+import {
+  addMiniProgramPageJson,
+  findChangedJsonFiles,
+} from '../src/json/mp/jsonFile'
+
+describe('miniProgram:jsonFile', () => {
+  const filename = 'pages/index/index'
+  test(`usingComponents`, () => {
+    const usingComponents = {
+      subscribe: 'plugin://subscribeMsg/subscribe',
+      demo: '/components/demo/demo',
+    }
+    addMiniProgramPageJson(filename, {
+      usingComponents,
+    })
+    expect(JSON.parse(findChangedJsonFiles().get(filename)!)).toEqual({
+      usingComponents: {
+        subscribe: 'plugin://subscribeMsg/subscribe',
+        demo: '../../components/demo/demo',
+      },
+    })
+  })
+})