加载React Native：UnhandledPromiseRejectionWarning：错误：找不到模块'View'

Question

I'm trying to contribute to a testing library. The library should provide a wrapper for react-test-renderer like react-native-testing-library does.

In order to see if my code worked I wrote a simple unit test using the code I wrote for the library. Since this was the first test for React Native I added react-native as a dev dependency together with metro-react-native-babel-preset . Furthermore, I added the preset to babel.

{
  "presets": [
    [
      "env",
      {
        "targets": {
          "browsers": ["last 2 versions", "safari >= 7"]
        }
      }
    ],
    "react",
    "module:metro-react-native-babel-preset"
  ]
}

The library does its assertions using tape .

Now, every test ( npm test ) throws the error:

> node -r babel-register -r babel-polyfill source/test
/path/to/node_modules/babel-core/lib/transformation/file/options/option-manager.js:328
        throw e;
        ^

Error: Couldn't find preset "module:metro-react-native-babel-preset" relative to directory

When I remove the preset from the babel config, I get the error:

(node:1841) UnhandledPromiseRejectionWarning: Error: Cannot find module 'View'
    at Function.Module._resolveFilename (internal/modules/cjs/loader.js:581:15)
    at Function.Module._load (internal/modules/cjs/loader.js:507:25)
    at Module.require (internal/modules/cjs/loader.js:637:17)
    at require (internal/modules/cjs/helpers.js:22:18)
    at Object.get View [as View] (/path/to/node_modules/react-native/Libraries/react-native/react-native-implementation.js:165:12)
    at _callee7$ (/path/to/source/test.js:110:6)
    at tryCatch (/path/to/node_modules/babel-polyfill/node_modules/regenerator-runtime/runtime.js:65:40)
    at Generator.invoke [as _invoke] (/path/to/node_modules/babel-polyfill/node_modules/regenerator-runtime/runtime.js:303:22)
    at Generator.prototype.(anonymous function) [as next] (/path/to/node_modules/babel-polyfill/node_modules/regenerator-runtime/runtime.js:117:21)
    at step (/path/to/source/test.js:27:191)
(node:1841) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 3)
(node:1841) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
not ok 10 test exited without ending
  ---
    operator: fail
    at: process.<anonymous> (/path/to/node_modules/tape/index.js:90:19)
    stack: |-
      Error: test exited without ending
          at Test.assert [as _assert] (/path/to/node_modules/tape/lib/test.js:226:54)
          at Test.bound [as _assert] (/path/to/node_modules/tape/lib/test.js:77:32)
          at Test.fail (/path/to/node_modules/tape/lib/test.js:319:10)
          at Test.bound [as fail] (/path/to/node_modules/tape/lib/test.js:77:32)
          at Test._exit (/path/to/node_modules/tape/lib/test.js:191:14)
          at Test.bound (/path/to/node_modules/tape/lib/test.js:77:32)
          at process.<anonymous> (/path/to/node_modules/tape/index.js:90:19)
          at process.emit (events.js:194:15)

How can I get React Native components to run in my test in a library (and outside of an expo init or react-native init project?

EDIT: I found out that the repo is using Babel 6, which is why the metro preset doesn't seem to work. So I exchanged it for babel-preset-react-native and now I'm back to the initial error that View can't be found.

EDIT 2: package.json

  "scripts": {
    "lint": "eslint source && echo 'Lint complete.'",
    "typecheck": "npx -p typescript tsc --rootDir . source/test.js --allowJs --checkJs --noEmit --lib es6 --jsx react && echo 'TypeScript check complete.'",
    "ts": "npm run -s typecheck",
    "test": "node -r babel-register -r babel-polyfill source/test",
    "watch": "watch 'clear && npm run -s test | tap-nirvana && npm run -s lint && npm run -s typecheck' source",
    "precommit": "npm run -s test && npm run -s lint && npm run -s typecheck"
  },
  "devDependencies": {
    "@types/node": "10.12.27",
    "babel-cli": "6.26.0",
    "babel-eslint": "10.0.1",
    "babel-preset-env": "1.7.0",
    "babel-preset-react": "6.24.1",
    "babel-preset-react-native": "4.0.1",
    "babel-register": "6.26.0",
    "eslint": "5.14.1",
    "eslint-plugin-react": "7.12.4",
    "react": "16.8.3",
    "react-native": "0.58.5",
    "tap-nirvana": "1.1.0",
    "typescript": "3.3.3333",
    "watch": "1.0.2"
  },
  "dependencies": {
    "cheerio": "1.0.0-rc.2",
    "esm": "3.2.6",
    "react-dom": "16.8.3",
    "react-test-renderer": "16.8.3",
    "tape": "4.10.1"
  }

EDIT 3: Sorry, apparently I didn't include my code, even though it is a helpful for solving this problem. It's pretty basic. I'm just trying to render a <View /> using ReactTestRenderer .

import TestRenderer from 'react-test-renderer';
import { Text, View } from 'react-native';
import { describe } from 'riteway';

describe('renderReactNativeComponent', async assert => {
  const text = 'Foo';
  const component = TestRenderer.create(
    <View>
      <Text>{text}</Text>
    </View>
  );
  console.log(Text);

  assert({
    given: 'A React Native component',
    should: 'return a working react test renderer instance',
    actual: component.findByType('text'),
    expected: text
  });
});

Answer 1

According to the docs , " Starting from react-native version 0.38, a Jest setup is included by default when running react-native init." .

And

"react-native ships with a Jest preset, so the jest.preset field of your package.json should point to react-native. The preset is a node environment that mimics the environment of a React Native app. Because it doesn't load any DOM or browser APIs, it greatly improves Jest's startup time."

The point is that Jest is supposed to work with React-Native, and riteway isn't. When you run react-native init the following dependency is added: "jest-react-native" . And a jest preset is added to package.json :

"jest": {
   "preset": "react-native"
}

Apparently there isn't any preset for riteway yet.

Answer 2

Remove node modules and install again

rm -rf node_modules
npm install

Answer 3

你没有返回任何东西，你需要返回一个“视图”

Answer 4

You might want to just use the suggested example in https://reactjs.org/docs/test-renderer.html just to make sure nothing wrong with code you have written, then add up your own logic to improve it (Just an idea to debug it). May be add it up in https://snack.expo.io ? or github, I will help you debug.