How to Achieve 100% Code Coverage in Unit Testing MatSelectChange in Angular

A concise guide on unit testing `MatSelectChange` in Angular to achieve `100% code coverage` using Karma and Jasmine. Learn how to effectively test conditional logic in selection changes.
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Achieving 100% Code Coverage in Unit Testing MatSelectChange in Angular

Unit testing is a crucial aspect of software development that helps ensure your code functions as intended. In Angular applications, you often deal with components that react to user input, such as a dropdown menu using MatSelectChange. This article will guide you through the process of writing effective unit tests for a method that behaves differently based on the selected value from a dropdown menu.

Understanding the Problem

Suppose you have a method that executes different actions depending on the value selected in a mat-select dropdown. Your goal is to test this method thoroughly to ensure all parts of the code are executed, achieving 100% code coverage. Below is the method we will be working with:

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This method checks the value of matSelectChange and calls different service methods based on the selected value. To achieve comprehensive testing and ensure that all branches of the code are executed, we need to implement unit tests that cover each scenario.

Setting Up Your Test Environment

Before diving into writing the tests, make sure you have set up your testing environment with the required modules and services. You'll need to have the following configuration in your test setup:

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Make sure that ServiceClass is properly injected and available for your tests to function correctly.

Writing the Unit Tests

Next, let’s write unit tests to verify that the correct service method is called for each of the possible values of the matSelectChange. Below is how you can structure your tests using Karma and Jasmine:

Test for Value '1'

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Test for Value '2'

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Breakdown of the Test Code

Service Injection: Each test fetches an instance of ServiceClass so that we can spy on its methods.

Spying on Methods: By using spyOn(service, 'doSomething'), we are setting up a spy to track whether the method is called.

Triggering Changes: The triggerEventHandler simulates a user selecting a value in the dropdown, allowing us to test the logic without manual interaction.

Assertions: Finally, we use expect assertions to check that the appropriate method was called with the expected parameters.

Conclusion

By following this structured approach, you can ensure that your unit tests for MatSelectChange provide 100% code coverage. This not only guarantees that all logic branches are tested but also enhances the reliability of your code. Remember, effective unit testing helps maintain high code quality and speeds up the development process in the long run.

Happy coding!