How to test React Native Module?

Question

I developed a React Native module (wrapping an SDK) and I’m interested in creating some unit tests using mocha. I’m not very familiar with mocha, but I can’t exactly figure out how to proceed.

I have my react native module, call it react-native-mymodule which I can use in an app by doing:

npm install react-native-mymodule

react-native link react-native-mymodule

Then I can import my module with:

import MySDK from "react-native-mymodule”;

I’m trying to do a similar thing with unit tests. In my root directory I have a test/ directory which is where I want to hold all my unit tests.

My simple test file in test/sdk.tests.js

import MySDK from "react-native-mymodule”;
var assert = require('assert');


describe(‘MySDK’, function() {
  describe('#indexOf()', function() {
    it('should return -1 when the value is not present', function() {
      assert.equal([1, 2, 3].indexOf(4), -1);
    });
  });
});

I’ve tried modifying a tutorial I found online on compiling modules, but haven’t had any luck. This is a file test/setup.js:

import fs from 'fs';
import path from 'path';
import register from 'babel-core/register';

const modulesToCompile = [
  'react-native-mymodule’
].map((moduleName) => new RegExp(`${moduleName}`));


const rcPath = path.join(__dirname, '..', '.babelrc');
const source = fs.readFileSync(rcPath).toString();
const config = JSON.parse(source);
config.ignore = function(filename) {
  if (!(/\/node_modules\//).test(filename)) {
    return false;
  } else {
    return false;
  }
}

register(config);

.babelrc in the root level of my module

{
  "presets": ["flow", "react-native"],
    "plugins": [
      ["module-resolver", {
        "root": [ "./js/" ]
      }]
    ]
}

I have a test/mocha.opts file:

--require babel-core/register
--require test/setup.js

I’m invoking mocha with: ./node_modules/mocha/bin/mocha and I get an error:

Error: Cannot find module 'react-native-mymodule'

Can anyone advise me on the best way to test react native modules?

Answer 1

If you want to test native modules, I suggest the following:

1. E2E Tests

Node.js standalone cannot interpret native modules. If you want to test native modules in the context of your app, you want to create e2e tests using appium/webdriverio instead of writing unit tests with mocha.

With this, you actually start an emulator with your app installed.

Resources:

• http://appium.io/docs/en/about-appium/intro/?lang=de
• https://medium.com/jetclosing-engineering/react-native-device-testing-w-appium-node-and-aws-device-farm-295081129790
• https://medium.com/swlh/automation-testing-using-react-native-and-appium-on-ubuntu-ddfddc0c29fe
• https://webdriver.io/docs/api/appium.html

2. Unit Tests

If you want to write unit tests for your native module, write them in the Language the Native Module is written in

Resources:

• https://www.swiftbysundell.com/basics/unit-testing/
• https://junit.org/junit5/
• https://developer.apple.com/documentation/xctest
• https://cmake.org/cmake/help/latest/manual/ctest.1.html

---

Other than that, you have to mock the modules.

• https://jestjs.io/docs/en/mock-functions
• https://sinonjs.org/releases/latest/mocks/
• https://www.npmjs.com/package/mock-require