Static mock not working

Question

I have the following sample unit test that tries to mock java.nio.file.Files but this mock does not work and the code attempts to delete the sample path.

@Test
    public void testPostVisitDirectory() throws Exception {
        Path mockedPath = Paths.get("sample path");
        PowerMockito.mockStatic(Files.class);
        PowerMockito.doNothing().when(Files.class,
                PowerMockito.method(Files.class, "delete", Path.class));

        DeleteDirVisitor visitor = new DeleteDirVisitor(false);
        Assert.assertEquals("The was a problem visiting the file",
                FileVisitResult.CONTINUE,
                visitor.postVisitDirectory(mockedPath, null));
    }

Any idea what is wrong?

this is the content of the method visitor.postVisitDirectory

[...]
if (e == null) {
            Files.delete(dir);
            return FileVisitResult.CONTINUE;
        }
[...]

Thanks,

Answer 1

I had a similar problem using powermock 1.5.1 and the Files class and suspect it has a problem static mocking some/all jdk1.7 classes, although I don't know why. I also checked javassist version and at the time it was latest (3.18.0-GA),

I stripped my class under test to just the Files line and it still did not work. I then decided to try to mock another static class, StringUtils.chop("string"); (commons-lang3) and then my powermock test worked and I was able to force it to generate an exception from mock.

This proved to me that I'd done everything by the book and that static mocking didn't work on Files class but it did on StringUtils.

By the way I changed, both, the @PrepareForTest and the PowerMockito.mockStatic() calls to reference the correct class.

In the end I gave up mocking Files. Just a heads-up in case anyone else has the same problem.

EDIT. Got it working: I have since tried this again as I needed it in another project. There is a newer version of PowerMock out (1.5.3) which uses an updated javassist (3.18.1-GA) that fixes a bug I mentioned in my response to another comment.

I can consistently get mocking of Files to work by adding the class under test to @PrepareForTest as well as Files now even if the class you are testing does not expose static methods. I hadn't needed to do this before for other static mocking. I don't know why it's needed or works differently for Files.

Example:

public class MyTestClass {

    public void justToTestMocking(Path path) throws IOException {
        if (!Files.exists(path)) {
            throw new IllegalArgumentException("I know there is a deleteIfExists() but I am just testing mocking");
        }
        Files.delete(path);
    }
}

And the test below:

@RunWith(PowerMockRunner.class)
@PrepareForTest({Files.class, MyTestClass.class})
public class MyTestClassTest {

    @Before
    public void setUp() {
        mockStatic(Files.class);

    }        

    @Test
    public void justToTestMocking_WillDeletePath() throws IOException {
        Path path = mock(Path.class);
        MyTestClass test = new MyTestClass();

        when(Files.exists(path)).thenReturn(true);

        test.justToTestMocking(path);

        verifyStatic();
        Files.delete(path);
    }
}

Answer 2

Did you add

@RunWith(PowerMockRunner.class)
@PrepareForTest(Files.class)

to your junit test class containing that method?

See powermock docs, the Writing tests section.

EDIT:

Hmmm, it seems like you're doing everything right. Here's what I'm running:

import java.io.IOException;
import java.nio.file.FileVisitResult;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.SimpleFileVisitor;

import org.junit.Assert;
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;

@RunWith(PowerMockRunner.class)
@PrepareForTest(Files.class)
public class TestVisitor {
  public class PrintingVisitor extends SimpleFileVisitor<Path> {
    @Override
    public FileVisitResult postVisitDirectory(final Path dir, final IOException exc) throws IOException {
      Files.delete(dir);
      return FileVisitResult.CONTINUE;
    }
  }

  @Test
  public void testPostVisitDirectory() throws Exception {
    final Path mockedPath = Paths.get("sample path");

    /* Mocking */
    PowerMockito.mockStatic(Files.class);
    PowerMockito.doNothing().when(Files.class, PowerMockito.method(Files.class, "delete", Path.class));
    /* End Mocking */

    final PrintingVisitor visitor = new PrintingVisitor();
    Assert.assertEquals("The was a problem visiting the file", FileVisitResult.CONTINUE, visitor.postVisitDirectory(mockedPath, null));
  }
}

If I comment out the section labeled Mocking I get the NoSuchFileException. If I leave it, the test passes.

Perhaps post complete example which produces the error?