How to Mock a Single Static Method and Return an Object Using PowerMockito?

Mocking a Single Static Method and Returning an Object Using PowerMockito

In this scenario, you aim to mock a static method, m1, from a class containing two static methods, m1 and m2. The goal is for m1 to return an object when called.

To achieve this, you initially attempted to use PowerMockito.mockStatic with a custom Answer to set the return value for m1. However, this approach resulted in a type mismatch error because it invoked both m1 and m2, which had different return types.

You also tried using PowerMockito.when to specify the return value for m1 directly. This, however, did not take effect when m1 was subsequently called.

The correct strategy is to utilize both the 1-argument version of mockStatic to enable static mocking and the when-thenReturn syntax to specify the return value for the targeted method. Here's how:

import static org.mockito.Mockito.*;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.invocation.InvocationOnMock;
import org.mockito.stubbing.Answer;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;

class ClassWithStatics {
  public static String getString() {
    return "String";
  }

  public static int getInt() {
    return 1;
  }
}

@RunWith(PowerMockRunner.class)
@PrepareForTest(ClassWithStatics.class)
public class StubJustOneStatic {
  @Test
  public void test() {
    PowerMockito.mockStatic(ClassWithStatics.class);

    when(ClassWithStatics.getString()).thenReturn("Hello!");

    System.out.println("String: " + ClassWithStatics.getString());
    System.out.println("Int: " + ClassWithStatics.getInt());
  }
}

In this example, ClassWithStatics contains two static methods: getString and getInt. The test class, StubJustOneStatic, uses PowerMockito to enable static mocking for ClassWithStatics and then stubs the return value of getString to "Hello!" using when-thenReturn. The default behavior for getInt is preserved, so it continues to return 1.

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