import java.util.Random;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;    }}

PowerMock:

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();    }}

 

 

http://codego.net/368377/