How to mock static methods

Here’s how to mock static methods step-by-step using Mockito (version 3.4 or higher, or 4.x/5.x) and JUnit 5.

✅ Requirements

• Mockito version ≥ 3.4.0
• JUnit 5
• Add the following dependencies:

<!-- For Maven -->
<dependency>
    <groupId>org.mockito</groupId>
    <artifactId>mockito-core</artifactId>
    <version>5.10.0</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.mockito</groupId>
    <artifactId>mockito-inline</artifactId>
    <version>5.10.0</version>
    <scope>test</scope>
</dependency>

Or for Gradle:

testImplementation 'org.mockito:mockito-core:5.10.0'
testImplementation 'org.mockito:mockito-inline:5.10.0'

🧪 Example: Mocking a Static Method

Suppose you have a static utility class:

public class Utils {
    public static String getEnv() {
        return System.getenv("APP_ENV");
    }
}

And a class using it:

public class AppService {
    public String getEnvironmentMessage() {
        String env = Utils.getEnv();
        return "Environment: " + env;
    }
}

✅ Mock Static Method in Test

import org.junit.jupiter.api.Test;
import org.mockito.MockedStatic;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.mockito.Mockito.*;

public class AppServiceTest {

    @Test
    void testGetEnvironmentMessageWithMockedStatic() {
        try (MockedStatic<Utils> mockedStatic = mockStatic(Utils.class)) {
            mockedStatic.when(Utils::getEnv).thenReturn("PRODUCTION");

            AppService service = new AppService();
            String result = service.getEnvironmentMessage();

            assertEquals("Environment: PRODUCTION", result);
        }
    }
}

✅ Key Points

• Use try (MockedStatic<YourClass> ...) for proper resource cleanup
• Static mocking is temporary and thread-safe inside the block

⚠️ Limitations

• Works only with Mockito-inline
• Avoid overusing static mocking—it often signals a need for better design (e.g., dependency injection)

🔥 Bonus: Mocking Static Methods in Legacy Code

If you're dealing with very old Java code or using Java versions < 8, consider PowerMock. But for modern Java and Mockito, prefer the inline method as above.

📦 Summary