Jest

Content

Jest tests are simple and target mostly API communication and methods and functions stability and correctness of execution.

To learn more about Jest, check this page.

All the tests are located in __tests__.

Each created test file should follow the next template: testName.test.ts.

Adding tests

To add a test, create a file by following previously mentioned template.

Describe your tests like so (I'll use localization as example):

describe("Localization", () => {

});

And add tests itself:

  test("Current language: EN", () => {
    expect(getLanguage()).toBe("en");
  });

  test("Current interface language: EN", () => {
    expect(getInterfaceLanguage()).toBe("en");
  });

  test("Set empty language", () => {
    setLanguage();
    expect(getLanguage()).toBe("en");
  });

  test("Set language: EN", () => {
    setLanguage(Languages.en);
    expect(getLanguage()).toBe("en");
  });

Running tests

You can run individual tests while debugging them in your IDE or if you want to run every single described test you can simply run: npm run tests. Which will show you PASSSED and FAILED tests.

Mocks

Some dependencies or environments require you to be mocked since tests are not running in React Native environment but NodeJS.

For these cases there is a folder called __mocks__.

There's already a simple mock of Localization:

import LocalizedStringsCore from "react-localization";

function getInterfaceLanguage() {
  return "en";
}

export default class LocalizedStrings extends LocalizedStringsCore {
  constructor(props) {
    super(props, getInterfaceLanguage);
  }
}

It defines that default and used language will be English without trying to get it from the system.

Then this mock is "imported" or better to say "mocked" in __tests__/localization.test.ts:

jest.mock("react-native-localization");

Coverage

To check how well you covered files with test you can see it using coverage.

Run npm run tests:coverage.

The coverege folder will appear which will give you HTML pages with detailed information, also there will be a print into terminal after the command will be executed.