How to unit test a class which uses Google Guice?

sadbutterfly

I have a class which uses google guice to inject dependencies. I want to write a unit test for this class, but I'm not sure how to go about it. Can anyone give me some pointers?

goldengorilla

Assuming you are looking for how to unit test a class which uses Google Guice Dependency Injection, here are a few things you can do:

First, you will want to create a test module which binds all of the dependencies that your class under test will need. You can do this by creating a module which extends com.google.inject.AbstractModule and overriding the configure() method. In this method, you will want to bind all of the dependencies that your class under test needs.

Next, you will want to create a test injector. To do this, you will need to create a com.google.inject.Injector and passing in your test module to the injector's createInjector() method.

Once you have your test injector, you can then use it to inject dependencies into your class under test. To do this, you will need to get the instance of your class under test from the injector, and then call the injector's injectMembers() method passing in your class under test.

You can then proceed to write your unit tests as normal.

For more information, please see the following links:

https://github.com/google/guice/wiki/TestingWithGuice
http://tothepointdevelopment.be/blog/2012/01/24/unit-testing-w-guice/

Adrian926

There is no one-size-fits-all answer to this question, as the best way to unit test a class which uses Google Guice will vary depending on the specifics of the class and the features of Google Guice being used. However, here are some general tips that may be helpful:

Make sure your test classes have access to the necessary Guice objects, either by injecting them via @Inject or by manually creating them.
When testing classes that use Guice's assisted inject feature, be sure to mock out the factory interface that is used to create the injected objects.
Be aware of the different ways that Google Guice can create objects (e.g. via @Provides methods, bind() statements, etc.), and unit test accordingly.
If possible, avoid testing classes that make use of Guice's @ImplementedBy annotation, as this can complicate things unnecessarily.

For more information on unit testing with Google Guice, you may find the following resources helpful:

The official Google Guice wiki page on unit testing: https://github.com/google/guice/wiki/UnitTesting
A blog post by Tim McCune on unit testing with Guice: http://blog.timmcune.com/2011/01/unit-testing-with-guice.html