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  • Writer's pictureRobin Alex Panicker

Testing Kotlin based Android Apps

Testing Kotlin based Android Apps

Testing is an integral part of the software development process, and Android app development is no exception. Kotlin, being the official programming language for Android development, provides developers with powerful tools and frameworks for testing Android apps.

In this blog, we will explore various testing strategies and best practices for testing Kotlin Android apps, ensuring high-quality and robust applications.

1. Setting up the Testing Environment

Before diving into testing, you need to set up the testing environment for your Kotlin Android app. This involves adding the necessary dependencies and libraries and determining the types of tests you'll perform.

1.1. Dependencies and Libraries

To enable testing, include the following dependencies in your app's build.gradle file:

dependencies {
    // Testing dependencies
    testImplementation 'junit:junit:4.13.2'
    androidTestImplementation 'androidx.test:runner:1.4.0'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
    // Other dependencies...

1.2. Test Types

There are three main types of tests in Android app development:

  • Unit Tests: Focus on testing individual components in isolation, such as functions, classes, or modules.

  • Instrumented Tests: Run on an Android device or emulator and interact with the app's UI components and resources.

  • Automated UI Tests: Similar to instrumented tests but are written to simulate user interactions and test user flows automatically.

Now that the testing environment is set up let's move on to the different testing strategies.

2. Unit Testing

Unit testing involves testing individual components of your app in isolation to ensure that they function correctly.

2.1. Introduction to Unit Testing

Unit tests focus on testing small units of code, such as individual functions or classes. They help identify bugs early in the development process, improve code maintainability, and provide fast feedback during development.

2.2. Writing Unit Tests in Kotlin

To write unit tests in Kotlin, you can use the JUnit testing framework. Write test methods that assert the expected behavior of the code being tested.

For example, test a function that calculates the sum of two numbers:

import org.junit.Test
import org.junit.Assert.assertEquals

class MathUtilsTest {
    fun testSum() {
        val result = MathUtils.sum(2, 3)
        assertEquals(5, result)

2.3. Using Mockito for Mocking Dependencies

Sometimes, unit tests require mocking dependencies to isolate the code being tested. Mockito is a popular mocking framework that simplifies the creation of mock objects. It allows you to define the behavior of mock objects and verify interactions with them.

For example:

import org.junit.Test
import org.junit.Assert.assertEquals
import org.mockito.Mockito.*

class UserManagerTest {
    fun testUserCreation() {
        val userService = mock(
        val userManager = UserManager(userService)
        `when`(userService.createUser("John Doe")).thenReturn(User("John Doe"))
        val user = userManager.createUser("John Doe")
        assertEquals("John Doe",
        verify(userService).createUser("John Doe")

2.4. Running Unit Tests

To run unit tests, right-click on the test class or package in Android Studio and select "Run 'ClassName'" or "Run 'PackageName'." You can also use Gradle commands like ./gradlew test to run tests from the command line.

3. Instrumentation Testing

Instrumentation tests allow you to test your app's behavior on an Android device or emulator. These tests interact with the app's UI components, resources, and the Android framework.

3.1. Introduction to Instrumentation Testing

Instrumentation tests are essential for verifying the correct behavior of your app's UI and interactions with the underlying system. They help catch bugs related to UI rendering, user input handling, and inter-component communication.

3.2. Writing Instrumented Tests in Kotlin

To write an instrumented test in Kotlin, use the androidx.test framework. Create a test class and annotate it with @RunWith(AndroidJUnit4::class). Use the @Test annotation on individual test methods.

For example:

import androidx.test.ext.junit.runners.AndroidJUnit4
import androidx.test.rule.ActivityTestRule
import org.junit.Assert.assertEquals
import org.junit.Rule
import org.junit.Test
import org.junit.runner.RunWith

class MainActivityInstrumentedTest {
    val activityRule = ActivityTestRule(
    fun testButtonClick() {
        val appContext = InstrumentationRegistry.getInstrumentation().targetContext
        // Simulate a button click
        // Verify the expected text is displayed
       onView(withId("Button Clicked")))

3.3. Running Instrumented Tests

To run instrumented tests, right-click on the test class or package in Android Studio and select "Run 'ClassName'" or "Run 'PackageName'." You can also use Gradle commands like ./gradlew connectedAndroidTest to run instrumented tests from the command line.

3.4. Interacting with UI Elements

The androidx.test.espresso library provides a fluent and expressive API for interacting with UI elements in instrumented tests. Use methods like onView, perform, and check to find views and perform actions on them.

For example, onView(withId( simulates a click on a button with the specified ID.

3.5. Using Espresso for UI Testing

Espresso is a popular testing framework within androidx.test.espresso for UI testing. It simplifies writing concise and readable tests for Android UI components. Espresso provides a rich set of matchers, actions, and assertions.

For more details, visit the link provided at the end of this blog [1].

4. Automated UI Testing

Automated UI tests, also known as end-to-end tests, simulate user interactions and test user flows automatically. These tests ensure that different parts of the app work together correctly.

4.1. Introduction to Automated UI Testing

Automated UI tests simulate user interactions, such as button clicks, text input, and gestures, to test the app's behavior and flow. These tests help catch integration issues, data flow problems, and user experience regressions.

4.2. Writing Automated UI Tests in Kotlin

To write automated UI tests in Kotlin, you can use frameworks like Espresso or UI Automator. Create test classes and use the testing APIs to interact with UI elements and perform actions.

For example:

import androidx.test.espresso.Espresso.onView
import androidx.test.espresso.assertion.ViewAssertions.matches
import androidx.test.espresso.matcher.ViewMatchers.withId
import androidx.test.espresso.matcher.ViewMatchers.withText
import org.junit.Test

class MainActivityAutomatedTest {
    fun testButtonClick() {
        // Simulate a button click
        // Verify the expected text is displayed
       onView(withId("Button Clicked")))

4.3. Running Automated UI Tests

To run automated UI tests, follow the same process as running instrumented tests. Right-click on the test class or package in Android Studio and select "Run 'ClassName'" or "Run 'PackageName'." Use Gradle commands like ./gradlew connectedAndroidTest to run tests from the command line.

4.4. Testing Navigation and User Flows

Automated UI tests are ideal for testing navigation and user flows within your app. Simulate user interactions to move between screens, verify correct data flow, and validate the expected behavior at each step.

5. Test Doubles and Dependency Injection

Test doubles are objects used in place of real dependencies during testing. Dependency Injection (DI) helps manage dependencies and facilitates the use of test doubles.

5.1. Understanding Test Doubles

Test doubles include stubs, mocks, fakes, and dummies. They allow you to isolate code under test, simulate specific behaviors, and verify interactions. Use test doubles to replace external dependencies or collaborator objects.

5.2. Using Dependency Injection for Testability

Design your app with dependency injection principles in mind. Dependency injection frameworks like Dagger or Koin can help manage dependencies and make testing easier. Inject test doubles instead of real dependencies during testing.

5.3. Mocking Dependencies with DI Containers

DI containers, such as Mockito or Koin, provide mechanisms to define test-specific configurations and replace real dependencies with test doubles. Use these containers to inject mock objects and stub behaviors.

5.4. Configuring Test-Specific Dependencies

Configure your DI container to provide test-specific dependencies when running tests. This allows you to control the behavior of dependencies during testing and ensure predictable test results.

6. Test Coverage and Continuous Integration

Test coverage measures the extent to which your code is tested by your test suite. Continuous Integration (CI) ensures that your tests are run automatically and regularly as part of your development workflow.

6.1. Measuring Test Coverage

Use tools like JaCoCo or Android Studio's built-in code coverage to measure test coverage. Aim for high code coverage to ensure that critical parts of your app are adequately tested.

6.2. Configuring Continuous Integration (CI)

Set up a CI system, such as Jenkins, Travis CI, or CircleCI, to automatically build and test your app. Configure your CI pipeline to run your tests and generate test reports.

6.3. Running Tests on CI Platforms

Configure your CI system to execute your tests during the build process. Ensure that your build script or CI configuration includes the necessary commands to run unit tests, instrumented tests, and automated UI tests.

7. Using APM Tools

APM tools play a crucial role in monitoring and analyzing the performance and stability of your Kotlin Android apps. They provide real-time insights into crashes, errors, and performance bottlenecks, helping you identify and resolve issues quickly.

Some of the popular APM tools for Android apps are Bugsnag, Finotes, New Relic and Sentry.

8. Testing Best Practices

Follow these best practices to write effective and maintainable tests for your Kotlin Android apps:

8.1. Isolating Tests

Each test should be independent and not rely on the state or side effects of other tests. Isolate tests to prevent dependencies between them, ensuring consistent and reliable results.

8.2. Writing Readable and Maintainable Tests

Write tests that are easy to understand and maintain. Use descriptive method and variable names, organize tests logically, and avoid duplicating code across tests.

8.3. Using Test Fixtures

Test fixtures are preconditions or shared resources required for multiple tests. Use setup and teardown methods, annotations, or test fixture classes to set up common test conditions and clean up resources.

8.4. Test-Driven Development (TDD)

Consider Test-Driven Development as a development practice. Write tests before implementing functionality. This approach helps define the desired behavior, ensures testability, and provides quick feedback.

8.5. Performance Testing

Consider performance testing to identify bottlenecks and optimize critical parts of your app. Measure performance metrics, such as response times or memory usage, to ensure your app meets performance expectations.

8.6. Edge Cases and Boundary Testing

Test edge cases and boundary conditions, such as maximum and minimum input values or error scenarios. These tests help uncover potential issues related to limits, constraints, or exceptional situations.


In this blog, we explored various testing strategies for Kotlin Android apps. We covered unit testing, instrumentation testing, automated UI testing, test doubles, dependency injection, test coverage, continuous integration, APM tools, and best practices.

By incorporating these testing strategies into your development process, you can ensure high-quality, robust, and reliable Kotlin Android apps. Remember to continuously iterate and improve your test suite to catch bugs early and deliver exceptional user experiences.

  1. Testing Jetpack Compose based Android UI using Espresso.

Blog for Mobile App Developers, Testers and App Owners


This blog is from Finotes Team. Finotes is a lightweight mobile APM and bug detection tool for iOS and Android apps.

In this blog we talk about iOS and Android app development technologies, languages and frameworks like Java, Kotlin, Swift, Objective-C, Dart and Flutter that are used to build mobile apps. Read articles from Finotes team about good programming and software engineering practices, testing and QA practices, performance issues and bugs, concepts and techniques. 

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