Step #3: Adding Some Unit Test Dependencies

So far, all of the dependencies that we have been adding to our app have used the implementation keyword. Those dependencies become part of the main app.

However, our dependencies closure in app/build.gradle also has androidTestImplementation and testImplementation statements. These are for instrumented tests and unit tests, respectively:

Right now, we have just one testImplementation dependency, for JUnit. JUnit is the foundation of all Android unit tests and instrumented tests, so we will be writing JUnit-based tests for both types.

Technically, we do not need anything more than that for our unit tests. In practice, though, usually we add some more dependencies, ones that will help us test more effectively.

With that in mind, add these lines to the dependencies closure in app/build.gradle:

  testImplementation "org.mockito:mockito-inline:3.12.1"
  testImplementation "com.nhaarman.mockitokotlin2:mockito-kotlin:2.2.0"
  testImplementation 'org.jetbrains.kotlinx:kotlinx-coroutines-test:1.5.1'

The org.mockito:mockito-inline and com.nhaarman.mockitokotlin2:mockito-kotlin bring in Mockito and a Kotlin wrapper for Mockito. Mockito is a popular “mocking” library, allowing us to define ad hoc implementations of classes. Sometimes, we use these to test scenarios that would be difficult to test otherwise. Sometimes, we use these as “call recorders”, to see whether certain functions were called as part of our tests.

The org.jetbrains.kotlinx:kotlinx-coroutines-test library helps you test coroutines. The author hopes that this was not a surprise.

(if it was… surprise!)