Скачать или смотреть Resolving the NullInjectorError in Angular Testing

Discover how to fix the `NullInjectorError` in Angular tests with this step-by-step guide. Get your application back on track in no time!
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This video is based on the question https://stackoverflow.com/q/65006922/ asked by the user 'Georgi Dimitrov Dimitrov' ( https://stackoverflow.com/u/14580114/ ) and on the answer https://stackoverflow.com/a/65006993/ provided by the user 'Bojan Kogoj' ( https://stackoverflow.com/u/715458/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving the NullInjectorError in Angular Testing: A Step-by-Step Guide

As a beginner in Angular, encountering errors during testing can be frustrating. One common issue you might face is the NullInjectorError, which can halt your development progress. In this guide, we'll explore a specific instance of this error, understand what it means, and provide a clear, structured solution to resolve it.

Understanding the Problem

The error message you encountered was:

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This indicates that Angular's dependency injection system is unable to find a provider for a service (in this case, the Router) when you're trying to run tests with ng test. This often happens in unit tests where the Angular testing module doesn't have all the necessary dependencies imported.

The Context

In your situation, the error occurred while testing the TodosComponent, which depends on the Angular Router. Here is the relevant snippet from your test file:

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By only declaring the Router in the providers, you're missing out on important routing configuration needed during the test, specifically the RouterTestingModule.

Solution: Implementing RouterTestingModule

To resolve the NullInjectorError, you need to import the RouterTestingModule instead of declaring the Router directly. Here's how you can update your testing setup:

Step-by-Step Modification

Import the RouterTestingModule: At the top of your testing file, make sure to import RouterTestingModule.

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Update the TestBed Configuration: Modify the configureTestingModule method to include RouterTestingModule in the imports array rather than as a provider.

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Here’s how the modified code should look after incorporating the changes:

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Conclusion

By replacing the direct reference to the Router with RouterTestingModule, you effectively provide the necessary testing infrastructure for Angular's router. This common pitfall is easy to overlook, especially for those new to the framework, but now you have a solid understanding of how to resolve it.

Now, you can run your tests smoothly without encountering the NullInjectorError. Remember, testing is a significant part of development; it helps ensure your application behaves as expected!

Happy coding and testing! If you run into more issues, don't hesitate to seek help or consult the official Angular documentation for further guidance.