Kotlin JUnit Tests Not Recognized in Android Studio

Many Android developers often face an annoying issue: Kotlin JUnit tests not recognized in Android Studio. This happens when your test classes or methods do not appear in the test runner, or the IDE fails to detect them as valid JUnit tests. In this article, we will dive deep into the causes of this problem, how to fix it step by step, and provide complete code examples to help you run tests seamlessly in your Kotlin Android project.

1. Understanding the Problem

JUnit is the most commonly used testing framework in Android development. However, when working with Kotlin in Android Studio, you may notice that your test methods are grayed out or that the IDE shows “No tests were found”. This usually happens because:

• JUnit dependencies are missing or mismatched in build.gradle.
• Incorrect test annotations are used.
• The test class is not placed in the correct test directory (src/test or src/androidTest).
• Android Studio cache or Gradle sync issues.

2. Setting Up JUnit in Kotlin

Before running tests, ensure that your build.gradle file includes the correct dependencies. For unit tests, you need testImplementation, while for instrumentation tests, you need androidTestImplementation.

dependencies {
    // JUnit for unit tests
    testImplementation "junit:junit:4.13.2"

    // AndroidX test extensions
    androidTestImplementation "androidx.test.ext:junit:1.1.5"
    androidTestImplementation "androidx.test.espresso:espresso-core:3.5.1"
}

After adding these dependencies, click on Sync Project with Gradle Files in Android Studio.

3. Writing a Simple Kotlin JUnit Test

Let’s start with a simple example. Suppose you have a utility class Calculator with basic arithmetic operations. You want to test its add and subtract methods.

class Calculator {
    fun add(a: Int, b: Int): Int = a + b
    fun subtract(a: Int, b: Int): Int = a - b
}

Now, create a test class inside src/test/java/:

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

class CalculatorTest {

    private val calculator = Calculator()

    @Test
    fun testAddition() {
        val result = calculator.add(5, 3)
        assertEquals(8, result)
    }

    @Test
    fun testSubtraction() {
        val result = calculator.subtract(10, 4)
        assertEquals(6, result)
    }
}

If Android Studio recognizes this test correctly, you should see the green run icon beside each method. If not, continue with the next fixes.

4. Common Fixes for “JUnit Tests Not Recognized”

4.1. Check Gradle Configuration

Make sure your test source sets are correctly defined. In your build.gradle (app-level), add:

android {
    sourceSets {
        test.java.srcDirs += "src/test/java"
        androidTest.java.srcDirs += "src/androidTest/java"
    }
}

4.2. Use the Correct Annotations

Kotlin tests require @Test annotation from JUnit. Make sure you import:

import org.junit.Test

Not:

import org.testng.annotations.Test

4.3. Clear Cache and Restart

Sometimes the issue is caused by Android Studio cache. Try:

1. Go to File > Invalidate Caches / Restart.
2. Rebuild project using Build > Rebuild Project.

4.4. Ensure JDK Compatibility

JUnit requires at least Java 8. If your project is set to a lower version, update your gradle.properties or build.gradle:

compileOptions {
    sourceCompatibility JavaVersion.VERSION_1_8
    targetCompatibility JavaVersion.VERSION_1_8
}
kotlinOptions {
    jvmTarget = "1.8"
}

5. Example: Instrumentation Test in Kotlin

If you want to run Android-specific tests (UI tests), you need instrumentation tests under src/androidTest. Example:

import androidx.test.ext.junit.runners.AndroidJUnit4
import androidx.test.platform.app.InstrumentationRegistry
import org.junit.Assert.assertEquals
import org.junit.Test
import org.junit.runner.RunWith

@RunWith(AndroidJUnit4::class)
class ExampleInstrumentedTest {

    @Test
    fun useAppContext() {
        val appContext = InstrumentationRegistry.getInstrumentation().targetContext
        assertEquals("com.example.myapp", appContext.packageName)
    }
}

Here, you must run the test on an emulator or physical device, since it depends on the Android framework.

6. Troubleshooting Checklist

Issue	Possible Cause	Solution
Test class not recognized	Wrong directory	Place in src/test/java or src/androidTest/java
No tests found	Missing JUnit dependency	Add testImplementation "junit:junit:4.13.2"
Red underline on @Test	Wrong import	Use org.junit.Test not org.testng
Tests fail to run	JDK compatibility	Ensure jvmTarget = "1.8"
Gradle sync issues	Cache corruption	Invalidate Caches & Restart

7. Conclusion

When you encounter Kotlin JUnit tests not recognized in Android Studio, don’t panic. Most of the time, the issue lies in dependency setup, wrong annotations, or misconfigured Gradle source sets. By applying the fixes in this article, you can quickly resolve the issue and continue writing effective unit and instrumentation tests for your Android apps.

For further reading on unit testing in Android, check the official documentation: Android Unit Testing Guide.