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Testing Requirements

This project utilizes the Jest library to test React apps.

The tests should guide your development. The tests are not comprehensively testing all required features of the project. They should help you check if you're going in the right direction.

Goal

The goal of introducing tests within this project is to practice reading them, running them, and doing independent research to work with them.

It is more important to implement all the required features than it is to get the tests to pass.

Introduction

Snapshot tests are a kind of test that focus on validating the correctness of UI.

Snapshot Tests Unit Tests
Validate the correctness of how UI renders Validate the correctness of a small unit, such as a function
Can be written in JavaScript, using Jest Can be written in JavaScript, using Jest
Can simulate rendering one or more components Can simulate invoking one or more functions

Running Tests

We run the provided tests with this command:

$ yarn test

Running tests with this command puts us in watch mode. When running tests in watch mode, the terminal window becomes dedicated to watching for code changes and then re-running the tests after each code change.

When we run tests, the output will show our test passes, failures, warnings, etc.

In watch mode, we can use the following commands inside the terminal to control our terminal window:

› Press a to run all tests.
› Press f to run only failed tests.
› Press q to quit watch mode.

To stop running the tests while in watch mode, we press q.

Skipped Test Syntax

Usually, when we run tests, we run the entire test suite. Using the Jest library, we can skip running individual tests.

Our tests are comprised of describe blocks and test blocks.

test blocks that begin with this test.skip syntax are skipped:

    test.skip('some test description', () => {

To stop skipping this test, we can remove the .skip:

    test('some test description', () => {

Running Individual Tests

Instead of running the entire test suite, we can run one test file at a time. This is helpful when we need to focus on running one set of tests.

We run individual test files by providing a relative path to the test file.

For example, to run the Square.test.js file, we should run:

$ yarn test src/components/Square.test.js

We should always run tests from the project root directory. Unintended consequences happen if we cd into another folder and run tests there.

Reminder

Recall that our goal for using tests within this project is to practice reading them, running them, and doing independent research to work with them.

Running tests should help us check if we're going in the right direction. It is more important to implement all the required features than it is to get the tests to pass.

Wave 1

The wave 1 tests exist in the files:

  • src/components/Board.test.js
  • src/components/Square.test.js

The wave 1 tests verify that:

  • The Square and Board components are rendered and present on the screen
  • The Square component displays either an "x", an "O", or an empty string "".

Wave 2

The wave 2 tests exist in all three test files:

  • src/components/App.test.js
  • src/components/Board.test.js
  • src/components/Square.test.js

They are skipped by default. Modify the syntax to unskip them.

The wave 2 tests verify that:

  • Clicking on a square makes an "X" or "O" appear.
  • In the Square component, the prop named exactly onClickCallback is a function. When the Square is clicked, the onClickCallback function is called.

Hints

  • If the tests cannot find an element, consider checking the element selectors that the test use. Then, modify your components to match the selectors, so that the tests can find the right element.

Wave 3

The wave 3 tests only exist in src/App.test.js.

They are skipped by default. Modify the syntax to unskip them.

The wave 3 tests verify that:

  • If x wins, the text "Winner is x" appears
  • If o wins, the text "Winner is o" appears