Mock private static method of a java class using PowerMock

Narendra Kumar's blog

Mock private static method of a java class using PowerMock

In java, PowerMock library allows us to mock private static methods. I have created a small example to demo this.

pom.xml

Should have the following dependencies( you can replace the testing with junit if you're using junit instead of test-ng).

<dependency>
  <groupId>org.testing</groupId>
  <artifactId>testing</artifactId>
  <version>6.14.3</version>
  <scope>test</scope>
</dependency>
<dependency>
  <groupId>org.mockito</groupId>
  <artifactId>mockito-core</artifactId>
  <version>2.28.2</version>
  <scope>test</scope>
</dependency>
<dependency>
  <groupId>org.powermock</groupId>
  <artifactId>powermock-module-testing</artifactId>
  <version>2.0.0</version>
  <scope>test</scope>
</dependency>

<dependency>
  <groupId>org.powermock</groupId>
  <artifactId>powermock-api-mockito2</artifactId>
  <version>2.0.0</version>
  <scope>test</scope>
</dependency>

code

We want to test method rateMyCountry of class CountryRating. As we can see, this method uses a private static method. We want to mock this static priavte method isPresidentDumb.

public class CountryRating {
    public int rateMyCountry(String countryCode,UnitedNationsEfficiency uns) {
        if (isPresidentDumb(countryCode,uns)) {
            return 5;
        }
        return 10;
    }

    private static boolean isPresidentDumb(String countryCode, UnitedNationsEfficiency uns) {
        return false;
    }
}

public class UnitedNationsEfficiency{

}

Test code is as given below:

import org.mockito.Mock;
import org.mockito.ArgumentMatchers;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.testng.PowerMockTestCase;
import org.testng.annotations.Test;

import static org.fest.assertions.api.Assertions.assertThat;

@Test
@PrepareForTest({CountryRating.class})
public class CountryRatingTest extends PowerMockTestCase {
    @Mock
    private UnitedNationsEfficiency uns;

    private final CountryRating objectUnderTest = new CountryRating();

    public void testRateMyCountry() throws Exception {
        PowerMockito.spy(CountryRating.class);
        PowerMockito.doReturn(true).when(CountryRating.class, "isPresidentDumb",ArgumentMatchers.startsWith("IN"),ArgumentMatchers.refEq(uns));
        assertThat(objectUnderTest.rateMyCountry("IN",uns)).isEqualTo(5);
    }
}

Important things to observe in the test code above:

@PrepareForTest({CountryRating.class}) for the class(CountryRating here) containing the static private method that we want to mock.
PowerMockito.spy(CountryRating.class) for the class containing the static private method that we want to mock
PowerMockito.doReturn(true).when(CountryRating.class, "isPresidentDumb", ArgumentMatchers.startsWith("IN"),ArgumentMatchers.refEq(uns)), configure the private static method mock. We can see that since the static method isPresidentDumb is private and can not be accessed from the test code, it's name is passed as string.

Thanks for reading!