Thursday 28 February 2019

Loading React Native: UnhandledPromiseRejectionWarning: Error: Cannot find module 'View'

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"
  }



from Loading React Native: UnhandledPromiseRejectionWarning: Error: Cannot find module 'View'

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