AAA Pattern in Writing Test Cases

test_format.js

describe('test cases for Button component', () => {
  
  it('should call callback fn when onPress is fired', () => {
    
    /** Arrange **/
    const handleClick = jest.fn()
    
    const { getByTestId, toJSON } = render(
      <Button onPress={handleClick}>
        <Text>Test Button</Text>
      </Button>
    )

    /** Act:  perform the actual work of the test **/
    const buttonElement = getByTestId('touchableElement')
    fireEvent.press(buttonElement)

    /** Assert – verify the result **/
    expect(handleClick).toHaveBeenCalledTimes(1)
  
  })
})