Arrange / Act / Assert in tests

Arrange / Act / Assert in tests

Posted 2023-10-15

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If you have written tests before you are probably familiar with arrange / act / assert

They are the 3 main parts to a test.

  • in arrange you set up the test.
    • For example, create a blog post object to pass in as a prop, or set up some mocked functions
  • in act you run the unit under code
    • in other words: run the thing you're testing
    • For simple tests without interaction this can just be render(<YourComponent />
    • But for most tests the render(...) call will be more of arrange, and the act section will be interacting (e.g. with clicks on buttons or typing into text inputs)
  • in assert you run your assertions to check the result
    • with jest, this will be your expect(result).toBe(expectedResult) code
    • this can be either:
      • the returned result (from 'act'),
      • what it rendered (for React components
      • or maybe some side effect (did it call window.fetch? Were new cookies set? etc)
✅ copied
test('calls login function when login button is clicked', () => { // Arrange const mockLogin = jest.fn(); render(<LoginButton login={mockLogin} />); // Act const loginButton = getByText('Log In');; // Assert expect(mockLogin).toHaveBeenCalled(); });

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