How to use normalizeProxy method in Jest

In Jest you have to pass a function into expect(function).toThrow(<blank or type of error>).

Example:

test("Test description", () => {
  const t = () => {
    throw new TypeError();
  };
  expect(t).toThrow(TypeError);
});

Or if you also want to check for error message:

test("Test description", () => {
  const t = () => {
    throw new TypeError("UNKNOWN ERROR");
  };
  expect(t).toThrow(TypeError);
  expect(t).toThrow("UNKNOWN ERROR");
});

If you need to test an existing function whether it throws with a set of arguments, you have to wrap it inside an anonymous function in expect().

Example:

test("Test description", () => {
  expect(() => {http.get(yourUrl, yourCallbackFn)}).toThrow(TypeError);
});

Alternative version that worked for me with jest only:

let assignMock = jest.fn();

delete window.location;
window.location = { assign: assignMock };

afterEach(() => {
  assignMock.mockClear();
});

Reference: https://remarkablemark.org/blog/2018/11/17/mock-window-location/

Conditional statements create branches of code which may not be executed (e.g. if/else). This metric tells you how many of your branches have been executed.

I found the answer here

https://devhints.io/jest

test('it is raining', () => {
  expect(inchesOfRain()).toBeGreaterThan(0);
});

test.skip('it is not snowing', () => {
  expect(inchesOfSnow()).toBe(0);
});

Link on off doc

I used:

beforeEach(() => {
    jest.spyOn(global.Math, 'random').mockReturnValue(0.123456789);
});

afterEach(() => {
    jest.spyOn(global.Math, 'random').mockRestore();
})

It is easy to add and restores the functionality outside the tests.

I also had to add the moduleNameMapper to my jest configuration for my tsconfig path maps in order to get my tests to recognize the path maps I had setup. Something like this:

"moduleNameMapper": {
      "^yourPath/(.*)": "<rootDir>\\yourPath\\$1"
    }

Hopefully this will help someone down the line!

Node

If you want to run them directly through node, try to require jest and/or jest-runtime. Also give @types/jest a try as well.

Check Edit 2 for new info about this

Edit

@types/jest (jest-DefinitelyTyped) is definitely needed (or just one solution). If you install it (e.g., dev dependency), the IDE errors should go away. I just tried it on Webstorm, and it works.

Edit 2

The new Jest@20 Matchers (e.g., .resolves and .rejects) are still not defined in @types/jest. You can keep track of its status on the links below: https://github.com/DefinitelyTyped/DefinitelyTyped/pull/16645 https://github.com/DefinitelyTyped/DefinitelyTyped/issues/16803

It should be available soon, though!

Also, it doesn't seem possible to run it directly through node. Last night I tried a bunch of different things, but using jest is the way to go - it really uses node under the hood, so I thought it would be possible as well. @thymikee over your opened issue at GitHub made clear that it's not.

Edit 3

The new release (20.0.1) includes the newest Jest definitions.

Lint

this isn't in the scope of this specific problem, but it also helps

Are you using something like ESLint? If so, you'll need eslint-plugin-jest

Following the steps described in this page: https://www.npmjs.com/package/eslint-plugin-jest, you will basically need to add it as an ESLint plugin and set jest globals in the ESLint configuration:

{
  "env": {
    "jest/globals": true
  }
}

If you plan on supporting ES6 tests, you'll also need Babel and babel-jest plugin with the following jest configuration:

"transform": {
  "^.+\\.js$": "babel-jest"
}

Finally, for Typescript tests you'd need the @types/jest and ts-jest packages as well

Solution 1: Delete the android/app/build folder and try to build again. It should work

Solution 2: run npm i --save @react-native-community/cli-platform-android

Alternative version that worked for me with jest only:

let assignMock = jest.fn();

delete window.location;
window.location = { assign: assignMock };

afterEach(() => {
  assignMock.mockClear();
});

Reference: https://remarkablemark.org/blog/2018/11/17/mock-window-location/