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Testing React Apps (Automated Testing)

What is "Testing"?

  • Manual Testing

    • Write Code, preview, and test in browser
    • Very important: You see what your users will see
    • Error-prone: it's hard to test all possible combinations and scenarios

  • Automated Testing

    • Code that tests your code
    • You test the individual building blocks of your app
    • Very technical but allows you to test ALL building blocks at once

Different Kinds of Automated Tests

  • Unit Tests
    • Test the individual building blocks (functions, components) in isolation
    • Projects typically contain dozens or hundreds of unit tests
    • The most common/important kind of test
  • Integration Tests
    • Test the combination of multiple building blocks
    • Projects typically contain a couple of integration tests
    • Also important, but focus on unit tests in most cases
  • End-to-End (e2e) Tests
    • Test complete scenarios in your app as the user would experience them
    • Projects typically contain only a few e2e tests
    • Important but can also be done manually (partially)

What To Test

  • What? + How?
  • What?
    • Test the different building blocks
    • Unit Tests: The smallest building blocks that make up your app
  • How?
    • Test success and error cases, also test rare (but possible) results

Required Tools & Setup

  • We need a tool for running our tests and asserting the results
    • Jest
  • We need a tool for "simulating"(rendering) our React app / components
    • React Testing Library
  • Both tools are already set up for you when using create-react-app

Writing Tests - The Three "A"s

  • Arrange
    • Set up the test data, test conditions and test environment
  • Act
    • Run logic that should be tested (e.g. execute function)
  • Assert
    • Compare execution results with expected results

References