Unit Testing Android Apps with MockK
Article Summary
Emre Muhammet Engin from Getir tackles a truth bomb: if your code is hard to test, your design probably sucks. His deep dive into MockK shows Android developers how to fix that.
Unit tests should make up the majority of your test suite, but writing them requires proper architecture and the right tools. This guide walks through MockK, the Kotlin-native mocking library that's become essential for Android developers testing ViewModels, repositories, and domain layers in isolation.
Key Takeaways
- Use relaxed = true in MockK to return null/defaults without explicit stubbing
- coEvery handles suspend functions while every mocks regular synchronous methods
- Capture argument values with slot() to verify exact parameters passed to functions
- verify() checks call counts with atLeast, atMost, and exactly parameters
- verifyOrder() ensures mocked methods are called in the expected sequence
MockK gives Android developers the tools to write comprehensive unit tests by mocking dependencies, verifying behaviors, and capturing values without fighting Kotlin's type system.
About This Article
Android apps often decay over time when dependencies aren't managed well. This makes the code harder to test and maintain, especially across ViewModels, repositories, and domain layers.
Emre Muhammet Engin shows how to use MockK's relaxed mocking with coEvery for suspend functions and every for synchronous methods. This approach isolates the units you're testing from their real dependencies.
Developers can check test coverage using Android Studio's built-in tools. This lets them verify that unit tests actually cover all code paths and edge cases in their apps.