How to mock private method for testing using PowerMock?

Question

I have a class which I would like to test with a public method that calls private one. I'd like to assume that private method works correctly. For example, I'd like something like doReturn....when.... I found that there is possible solution using PowerMock, but this solution doesn't work for me. How It can be done? Did anybody have this problem?

Answer 1

I don't see a problem here. With the following code using the Mockito API, I managed to do just that :

public class CodeWithPrivateMethod {      public void meaningfulPublicApi() {         if (doTheGamble("Whatever", 1 << 3)) {             throw new RuntimeException("boom");         }     }      private boolean doTheGamble(String whatever, int binary) {         Random random = new Random(System.nanoTime());         boolean gamble = random.nextBoolean();         return gamble;     } } 

And here's the JUnit test :

import org.junit.Test; import org.junit.runner.RunWith; import org.powermock.api.mockito.PowerMockito; import org.powermock.core.classloader.annotations.PrepareForTest; import org.powermock.modules.junit4.PowerMockRunner; import static org.mockito.Matchers.anyInt; import static org.mockito.Matchers.anyString; import static org.powermock.api.mockito.PowerMockito.when; import static org.powermock.api.support.membermodification.MemberMatcher.method;  @RunWith(PowerMockRunner.class) @PrepareForTest(CodeWithPrivateMethod.class) public class CodeWithPrivateMethodTest {      @Test(expected = RuntimeException.class)     public void when_gambling_is_true_then_always_explode() throws Exception {         CodeWithPrivateMethod spy = PowerMockito.spy(new CodeWithPrivateMethod());          when(spy, method(CodeWithPrivateMethod.class, "doTheGamble", String.class, int.class))                 .withArguments(anyString(), anyInt())                 .thenReturn(true);          spy.meaningfulPublicApi();     } }