Question

Am trying to run this baseline unit test from Powermock. Running the code As-Is off of that link, with both Mockito and Junit and it runs without error. Unfortunately, I need Mockito and TestNG and that gives me errors on 6 out of the 10 tests:

Mockito cannot mock this class: class replica.java.util.UUID$$PowerMock5
Mockito can only mock visible & non-final classes.

Sorry this is a long code post, but I wanted to be complete. The first test passes, the second, 5th, 6th, 7th, 9th and 10th all fail. Can this be made to work under TestNG?

EDIT – add version numbers

These results occur with Mockito V1.9.0, Powermock V1.4.12, and TestNG v6.8 (all running under Java 1.7)

Here is the code with my minor modifications:

/*
 * Copyright 2008 the original author or authors.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import static org.mockito.BDDMockito.given;
import static org.mockito.Matchers.anyLong;
import static org.mockito.Mockito.times;
import static org.powermock.api.mockito.PowerMockito.doNothing;
import static org.powermock.api.mockito.PowerMockito.mock;
import static org.powermock.api.mockito.PowerMockito.mockStatic;
import static org.powermock.api.mockito.PowerMockito.spy;
import static org.powermock.api.mockito.PowerMockito.verifyStatic;
import static org.powermock.api.mockito.PowerMockito.when;

import java.net.URL;
import java.net.URLConnection;
import java.net.URLEncoder;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.UUID;

import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.testng.PowerMockObjectFactory;
import org.testng.Assert;
import org.testng.IObjectFactory;
import org.testng.annotations.ObjectFactory;
import org.testng.annotations.Test;

/**
 * Demonstrates PowerMockito's ability to mock non-final and final system
 * classes. To mock a system class you need to prepare the calling class for
 * testing. I.e. let's say you're testing class A which interacts with
 * URLEncoder then you would do:
 * 
 * <pre>
 * 
 * &#064;PrepareForTest({A.class})
 * 
 * </pre>
 */
// @RunWith(PowerMockRunner.class)
@PrepareForTest({ SystemClassUser.class })
public class SystemClassUserTest {

    @ObjectFactory
    public IObjectFactory getObjectFactory() {
        return new PowerMockObjectFactory();
    }

    @Test
    public void assertThatMockingOfNonFinalSystemClassesWorks() throws Exception {
        mockStatic(URLEncoder.class);

        when(URLEncoder.encode("string", "enc")).thenReturn("something");

        Assert.assertEquals("something", new SystemClassUser().performEncode());

    }

    @Test
    public void assertThatMockingOfTheRuntimeSystemClassWorks() throws Exception {
        mockStatic(Runtime.class);

        Runtime runtimeMock = mock(Runtime.class);
        Process processMock = mock(Process.class);

        when(Runtime.getRuntime()).thenReturn(runtimeMock);
        when(runtimeMock.exec("command")).thenReturn(processMock);

        Assert.assertSame(processMock, new SystemClassUser().executeCommand());
    }

    @Test
    public void assertThatMockingOfFinalSystemClassesWorks() throws Exception {
        mockStatic(System.class);

        when(System.getProperty("property")).thenReturn("my property");

        Assert.assertEquals("my property", new SystemClassUser().getSystemProperty());
    }

    @Test
    public void assertThatPartialMockingOfFinalSystemClassesWorks() throws Exception {
        spy(System.class);

        when(System.nanoTime()).thenReturn(2L);

        new SystemClassUser().doMoreComplicatedStuff();

        Assert.assertEquals("2", System.getProperty("nanoTime"));
    }

    @Test
    public void assertThatMockingOfCollectionsWork() throws Exception {
        List<?> list = new LinkedList<Object>();
        mockStatic(Collections.class);

        Collections.shuffle(list);

        new SystemClassUser().shuffleCollection(list);

        verifyStatic(times(2));
        Collections.shuffle(list);
    }

    @Test
    public void assertThatPartialMockingOfFinalSystemClassesWorksForNonVoidMethods() throws Exception {
        spy(System.class);

        when(System.getProperty("property")).thenReturn("my property");

        final SystemClassUser systemClassUser = new SystemClassUser();
        systemClassUser.copyProperty("to", "property");
    }

    @Test
    public void assertThatMockingStringWorks() throws Exception {
        mockStatic(String.class);
        final String string = "string";
        final String args = "args";
        final String returnValue = "returnValue";

        when(String.format(string, args)).thenReturn(returnValue);

        final SystemClassUser systemClassUser = new SystemClassUser();
        Assert.assertEquals(systemClassUser.format(string, args), returnValue);
    }

    @Test
    public void mockingStaticVoidMethodWorks() throws Exception {
        mockStatic(Thread.class);
        doNothing().when(Thread.class);
        Thread.sleep(anyLong());

        long startTime = System.currentTimeMillis();
        final SystemClassUser systemClassUser = new SystemClassUser();
        systemClassUser.threadSleep();
        long endTime = System.currentTimeMillis();
        Assert.assertTrue(endTime - startTime < 5000);
    }

    @Test
    public void mockingURLWorks() throws Exception {
        URL url = mock(URL.class);
        URLConnection urlConnectionMock = mock(URLConnection.class);

        when(url.openConnection()).thenReturn(urlConnectionMock);

        URLConnection openConnection = url.openConnection();

        Assert.assertSame(openConnection, urlConnectionMock);
    }

    @Test
    public void mockingUUIDWorks() throws Exception {
        // given
        final UUID mock = mock(UUID.class);
        mockStatic(UUID.class);
        given(UUID.randomUUID()).willReturn(mock);

        // when
        String actual = new SystemClassUser().generatePerishableToken();

        // then
        Assert.assertEquals("00000000000000000000000000000000", actual);
    }
}

---

If it helps out, here is a stripped down version that executes one of the failing tests:
[I wasn’t sure if I should have edited the question, I’m sorry if that is what I should have done, but where it was already too long, this approach seemed to make a bit more sense.]

import static org.powermock.api.mockito.PowerMockito.mockStatic;
import static org.powermock.api.mockito.PowerMockito.when;

import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.testng.PowerMockObjectFactory;
import org.testng.Assert;
import org.testng.IObjectFactory;
import org.testng.annotations.ObjectFactory;
import org.testng.annotations.Test;

@PrepareForTest({ SystemClassUser.class })
public class SystemClassUserTest {

@ObjectFactory
public IObjectFactory getObjectFactory() {
    return new PowerMockObjectFactory();
}

@Test
public void assertThatMockingOfFinalSystemClassesWorks() throws Exception {
    mockStatic(System.class);

    when(System.getProperty("property")).thenReturn("my property");

    Assert.assertEquals("my property", new SystemClassUser().getSystemProperty());
}
}

---

Now here is the SystemClassUser class similarly stripped down:

import java.io.IOException;

public class SystemClassUser {

    public String getSystemProperty() throws IOException {
        return System.getProperty("property");
    }

}

Running results in this Exception:

FAILED: assertThatMockingOfFinalSystemClassesWorks
org.mockito.exceptions.base.MockitoException:
Mockito cannot mock this class: class replica.java.lang.System$$PowerMock0
Mockito can only mock visible & non-final classes.

Answer 1

I simply modified test case to

public class SystemClassUserTest extends PowerMockTestCase {
    ...
}

and it works fine

---

edit (one year later): I recently found System Rules library, I didn’t try it with getProperty(), but System.exit() worked exactly as I expected…