expect (screen. In cases 2 and 3, we use queryByTestId instead of getByTestId.queryByTestId doesn't fail when the queried element doesn't exist, instead, it returns either a value or null and that's what we test with expect().toBeTruthy() and expect().toBeNull(). Using Enzyme with SystemJS. Jest is the best option for most React Native projects. Jest expect has a chainable .not assertion which negates any following assertion. toHaveTextContent (route) Reducing boilerplate # You can use the wrapper option to wrap a MemoryRouter around the component you want to … Jest is built into React, which makes Jest a simple, out-of-the-box solution to for React Native unit testing. This won’t be a deep dive into unit testing React components but I will present some options for mocking external services. When you import a package, you can tell Jest to “spy” on the execution of a particular function, using spyOn(), without affecting how that method works. Also all TypeScript files should be in a src folder which is always recommended (even without Jest… This is true for stub/spy assertions like .toBeCalled(), .toHaveBeenCalled(). As a bonus, Jest not only can unit test Reactive Native apps, but it can also unit test other JavaScript frameworks, such as Angular, Vue, Bable, TypeScript, and Node. Using Enzyme with Karma. Pastebin is a website where you can store text online for a set period of time. import Enzyme from 'enzyme' import Adapter from 'enzyme-adapter-react-16' Enzyme.configure({ adapter: new Adapter() }) package.json "jest": { "setupFiles": [ "test/setup.js" ] } This configures Enzyme for React v16, and Jest to automatically configure Enzyme for you. It’s possible to require/import and expose the real module while using jest.mock. expect (screen. There are other adapters in Enzyme’s installation instructions. Using Enzyme with Mocha. jest-enzyme with Jest. Using Enzyme with Browserify. Note: We assume you start off with a simple node package.json setup. Between test runs we need mocked/spied on imports and functions to be reset so that assertions don’t fail due to stale calls (from a … Jest documentation should-enzyme for should.js. expect-enzyme for expect. toHaveTextContent ('My Name Is: C3P0') * To test a component that provides a context value, render a matching * consumer as the child With Jasmine this is super easy — The application code: And the test code: What’s the equivalent with Jest? getByText (/^My Name Is:/)). jest.requireActual(moduleName) Returns the actual module instead of a mock, bypassing all checks on whether the module should receive a mock implementation or not. Example: const mathjs = require ( 'mathjs' ) test ( `The mathjs log function` , () => { const spy = jest . The Question : 316 people think this question is useful I want to test that one of my ES6 modules calls another ES6 module in a particular way. 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