Angular Unit testing: How to pass multiple files through include while running ng test from CLI?

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04-10-2024

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Angular Unit Testing: Passing Multiple Files with include in ng test

Angular's powerful testing framework makes it easy to write and run unit tests for your components, services, and other parts of your application. One common need is to test multiple files together, particularly when dealing with related components or services that interact closely. This is where the include option in the ng test command comes in handy. However, passing multiple files to include can be tricky. This article explains how to do it effectively.

The Problem: Passing Multiple Files to include

Imagine you have several related components - ComponentA, ComponentB, and ComponentC - that work together to form a complex UI element. Testing these components individually might be insufficient, as you want to ensure their interaction is correct. You might think that simply including all three in the include option would work:

ng test --include "src/app/component-a/component-a.component.spec.ts" --include "src/app/component-b/component-b.component.spec.ts" --include "src/app/component-c/component-c.component.spec.ts"

Unfortunately, this approach is not supported by Angular's CLI. It will only run the tests from the last file specified in the include option, effectively ignoring the others.

The Solution: Using Wildcards and Multiple include Flags

To achieve our goal of testing multiple files together, we need to take advantage of wildcards and multiple include flags:

1. Wildcard Inclusion: We can use wildcards like *.spec.ts to target all files ending with .spec.ts within a specific directory.

2. Multiple include Flags: By using separate include flags for each directory containing related test files, we can ensure all relevant tests are executed.

Here's how you would apply this approach:

ng test --include "src/app/component-a/*.spec.ts" --include "src/app/component-b/*.spec.ts" --include "src/app/component-c/*.spec.ts"

In this example, the --include flags will capture all test files within the respective component directories. Angular will then execute all of these tests together, providing a comprehensive view of the components' interactions.

Best Practices for Multiple File Testing

• Organize your test files: Keeping related test files in the same directory makes managing include options much easier.

• Use --watch for iterative development: Use the --watch flag to automatically rerun your tests whenever you make changes. This helps identify issues quickly during development.

• Consider using a test framework: Frameworks like Jasmine or Jest provide structure and utilities that simplify complex testing scenarios, especially when dealing with multiple files.

Conclusion

Passing multiple files to the include option in ng test requires a strategic approach using wildcards and multiple include flags. This technique empowers developers to test related components and services effectively, ensuring the integrity of their Angular applications. By following best practices for test file organization and leveraging tools like test frameworks, you can create robust and maintainable test suites for your Angular projects.