Introducing kotlin-test to our codebase

[Marcin Kozinski]

Hi all,

Today we landed our first ADR (Architectural Decision Record). It's about introducing a new test dependency: kotlin-test.

It's not a big library, but it provides some quality of life improvements for testing in Kotlin. It wraps the existing JUnit assertions you already know and use, and it adds a few new ones. Together they allow you to assert things in a more Kotlin-idiomatic way, enable better code analysis in the compiler and in Android Studio (e.g. smart casts after asserting something is not null or of a specific type) and in some cases improve the default messages when assertions fail.

I encourage you to use kotlin-test assertions in new and existing tests. They are fully interoperable with JUnit, so they can co-exist with JUnit assertions even in the same function. We will run migrations to update some existing assertions to kotlin-test where the improvements are greatest and add quick-fixes to Android Studio so you can learn about the new and improved APIs as you work on your tests.

kotlin-test has been available in libs.versions.toml and in Fenix tests for a couple of weeks. I also just landed a stack that added it to most of android-components. If you want to use it in a new component or an existing one where it isn't available yet, feel free to add it in build.gradle.

kotlin-test also provides @Test, @BeforeTest, @AfterTest and @Ignore annotations, which are actually just type aliases for JUnit annotations. They don't provide any real benefits for us right now. But we might migrate all annotations to kotlin-test later for consistency. Both work, but when in doubt stick to JUnit annotations for now.

If you have any questions, please let me know!

Best

Marcin