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Matt Williams for Tech Dev Blog

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Get Your Test On with Jasmine: The Happy Way to Ensure Quality

Get Your Test On with Jasmine: The Happy Way to Ensure Quality

Welcome to our tutorial on how to best use the Jasmine JavaScript testing library!

First things first, what is Jasmine and why should you use it? Jasmine is a behavior-driven development (BDD) framework for testing JavaScript code. It is designed to be easy to use and read, so that you can write and understand your tests quickly.

Now, let's get started with setting up Jasmine.

Setting up Jasmine

There are a few different ways to install and use Jasmine, but the most common method is to include it as a script in your HTML file. Here's an example of how to do this:

<!-- Include the Jasmine library -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/jasmine/3.6.3/jasmine.min.js"></script>

<!-- Include your JavaScript code -->
<script src="your-code.js"></script>

<!-- Include the Jasmine library for running the tests -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/jasmine/3.6.3/jasmine-html.min.js"></script>

<!-- Include the Jasmine library for running the tests in the browser -->
<script src="https://cdnjs.cloudflare.com/ajax/libs/jasmine/3.6.3/boot.min.js"></script>
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Alternatively, you can install Jasmine via npm by running the following command:

npm install --save-dev jasmine
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Once you have Jasmine set up, you're ready to start writing your tests!

Writing tests

Jasmine tests are written using a syntax called "expectations." An expectation is a statement that asserts something about the code you are testing. For example, you might expect a certain function to return a certain value, or you might expect a certain variable to be truthy.

Here's an example of an expectation:

expect(myFunction()).toEqual(5);
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In this example, we are expecting the result of calling myFunction() to be equal to 5. If it is, the test will pass. If it is not, the test will fail.

You can chain multiple expectations together in a single test, like this:

expect(myFunction()).toEqual(5);
expect(myOtherFunction()).toBeTruthy();
expect(myThirdFunction()).toBeDefined();
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Each of these expectations will be tested separately. If any of them fail, the entire test will fail.

Organizing your tests

Jasmine provides a few different ways to organize your tests. The most common method is to use "describe" blocks to group related tests together. Here's an example:

describe("My test suite", function() {
  it("should do something", function() {
    // Test code goes here
  });

  it("should do something else", function() {
    // Test code goes here
  });

  // ...
});
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In this example, we have a test suite called "My test suite" that contains two tests. You can nest describe blocks to create even more organization:

describe("My test suite", function() {
  describe("Test group 1", function() {
    it("should do something", function() {
      // Test code goes here
    });

    it("should do something else", function() {
      // Test code goes here
    });
  });

  describe("Test group 2", function() {
    it("should do something", function() {
      // Test code goes here
    });

    it("should do something else", function() {
      // Test code goes here
    });
  });

  // ...
});
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This allows you to group your tests in a logical way and make it easier to find specific tests when you need to.

Running your tests

Once you have your tests written, you'll want to run them to see if they pass or fail. There are a few different ways to do this, depending on how you set up Jasmine.

If you included the Jasmine library in your HTML file, you can simply open the file in a browser and the tests will run automatically. You'll see the results of the tests displayed on the page.

If you installed Jasmine via npm, you can use the jasmine command to run your tests. Just navigate to the directory where your tests are located and run the following command:

jasmine
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This will run all of the tests in the current directory and its subdirectories.

There are also a number of tools and frameworks that integrate with Jasmine and make it even easier to run your tests. Some popular options include Karma and Protractor.

Tips for writing effective tests

Now that you know the basics of how to use Jasmine, here are a few tips to help you write effective tests:

  • Make your tests independent: Each test should be able to run on its own and not depend on the results of other tests. This will make it easier to isolate and debug any issues that arise.
  • Test both positive and negative scenarios: Test that your code works as expected, but also test what happens when things go wrong. This will help ensure that your code is robust and can handle a wide range of inputs.
  • Keep your tests focused: Each test should test one specific thing. If you're testing a complex function, it might make sense to break it down into multiple tests that each focus on a specific aspect of the function's behavior.
  • Avoid testing implementation details: Instead of testing how your code is implemented, focus on what it does. This will make your tests more resilient to changes in your code and will allow you to make updates without having to update your tests.

We hope this tutorial has been helpful and has given you a good introduction to using the Jasmine JavaScript testing library. Happy testing!

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