Gain insights into Jest, a versatile testing framework. Learn about fundamental and advanced testing techniques, from unit tests to CI/CD integration, for comprehensive JavaScript application testing.

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Jest is a framework for testing applications developed in JavaScript. It has a well-documented and well-maintained range of tools to run tests in parallel. It is simple and works with projects using Babel, TypeScript, Node, React, Angular, Vue, etc. It works well for both client and server testing. 

This course covers Jest in-depth and is agnostic of any specific JavaScript framework. The course begins with the fundamentals of Jest testing, deconstructing the components of a test and covering how to compose basic unit tests and snapshot tests with Jest correctly. Next, it shows the testing of asynchronous code and the code that relies on external dependencies. Lastly, this course illustrates how Jest testing can effectively integrate into the real-world software development cycle through CI/CD pipeline.

It gives you hands-on experience in setting up Jest, types of testing, testing coverage, mocking, and native tooling depth.

…. To come 

… to come 

Mastering Jest: A Complete Guide to Testing

Which option is _not_ an available Jest matcher?


Which option is not an available Jest matcher?

**(True or False)** Additional matchers are made available through additional libraries.

(True or False) Additional matchers are made available through additional libraries.

```
expect.extend({
  customMatcher(x, y, z) {
    return {
      pass: true,
      message: () => 'test failed',
    };
  },
});
```

```
expect.extend({
  matcher: customMatcher(x, y, z),
  pass: true, 
  message: () => 'test failed',
});
```

```
expect.customMatcher = (x, y, z) => {
  return {
    pass: true,
    message: () => 'test failed',
  };
};
```

```
expect.extendMatchers({
  customMatcher(x, y, z) {
    return {
      pass: true,
      message: () => 'test failed',
    };
  },
});
```

Which code block has the correct syntax for declaring a custom matcher?

Which code block has the correct syntax for declaring a custom matcher?

```
expect(a).customMatcher(x, y, z).toBeTruthy();
```

```
expect(customMatcher(x, y, z)).toBeTruthy();
```

What is the proper syntax to invoke the custom matcher below?

```
expect.extend({
  customMatcher(x, y, z) {
    return {
      pass: true,
      message: () => 'test failed',
    };
  },
});
```

What is the proper syntax to invoke the custom matcher below?
<pre><code>expect.extend({
 customMatcher(x, y, z) {
 return {
 pass: true,
 message: () =&gt; 'test failed',
 };
 },
});
</code></pre>

<code>.toThrowErrorMatchingSnapshot()</code>

**(Select all that apply.)** Jest provides which error-specific matchers?


(Select all that apply.) Jest provides which error-specific matchers?

```
expect(() => isOne(4)).toBeFalsy();
```

Testing-specific error handling in JavaScript can be tricky. In order to assert on errors and avoid tests incorrectly passing when we expect them to throw, which pattern should we use for the function below?

```
const isOne = (x) => {
  if (x !== 1) {
    throw new Error('not equal to 1');
  }

  return true;
}
```



Testing-specific error handling in JavaScript can be tricky. In order to assert on errors and avoid tests incorrectly passing when we expect them to throw, which pattern should we use for the function below?
<pre><code>const isOne = (x) =&gt; {
 if (x !== 1) {
 throw new Error('not equal to 1');
 }

 return true;
}
</code></pre>

What can we test the inverse of a matcher with?


What can we test the inverse of a matcher with?

Introduction

Setting Up Jest

Jest Matchers

Writing Unit Tests

Writing Snapshot Tests

Asynchronous Code

Mocking

Mocking External Libraries

Working with Jest Mocks

Setup & Teardown

Test Coverage & CI/CD Pipelines

Test Coverage in Jest

Conclusion

Bonus: Best Practices

Bonus: Resources for Continued Learning

Appendix

Quiz on Jest Matchers