Mock System class to get system properties

问题:

I have a folder path set in system variable through JVM arguments in Eclipse and I am trying to access it in my class as: System.getProperty("my_files_path").

While writing junit test method for this class, I tried mocking this call as test classes do not consider JVM arguments. I have used PowerMockito to mock static System class and tried returning some path when System.getProperpty is being called.

Had @RunWith(PowerMockRunner.class) and @PrepareForTest(System.class) annotations at class level. However, System class is not getting mocked as a result I always get null result. Any help is appreciated.

回答1:

Thanks Satish. This works except with a small modification. I wrote PrepareForTest(PathFinder.class), preparing the class I am testing for test cases instead of System.class

Also, as mock works only once, I called my method right after mocking. My code just for reference:

@RunWith(PowerMockRunner.class)
@PrepareForTest(PathInformation.class)
public class PathInformationTest {

    private PathFinder pathFinder = new PathFinder();

@Test
    public void testValidHTMLFilePath() { 
        PowerMockito.mockStatic(System.class);
        PowerMockito.when(System.getProperty("my_files_path")).thenReturn("abc");
        assertEquals("abc",pathFinder.getHtmlFolderPath());
    }
}

回答2:

There are certain classes PowerMock can't mock in the usual way. See here:

• https://code.google.com/p/powermock/wiki/MockSystem

This, however, may still not work. In order of "good design" preference, you can fall back to these:

1. Refactor your code! Using a System property for passing a file path around is probably not the best way. Why not use a properties file loaded into a Properties object? Why not use getters/setters for the components that need to know this path? There are many better ways to do this.

   The only reason I could think of not to do this is you're trying to wrap a test harness around code you "can't" modify.

2. Use @Before and @After methods to set the System property to some known value for the test(s). You could even make it part of the @Test method itself. This will be FAR easier than attempting to mock through PowerMock. Just call System.setProperty("my_files_path","fake_path");

回答3:

Set the system property in your test and ensure that it is restored after the test by using the rule RestoreSystemProperties of the library System Rules.

public class PathInformationTest {
  private PathFinder pathFinder = new PathFinder();

  @Rule
  public TestRule restoreSystemProperties = new RestoreSystemProperties();

  @Test
  public void testValidHTMLFilePath() { 
    System.setProperty("my_files_path", "abc");
    assertEquals("abc",pathFinder.getHtmlFolderPath());
  }
}

回答4:

@RunWith(PowerMockRunner.class)
@PrepareForTest(System.class)
public class MySuperClassTest {   
@Test
public void test(){ 
    PowerMockito.mockStatic(System.class);
    PowerMockito.when(System.getProperty("java.home")).thenReturn("abc");
    System.out.println(System.getProperty("java.home"));
}
} 

回答5:

Sailaja add System.class because as per the power mock guidelines for static,private mocking you should add the class in prepare for test.

 @PrepareForTest({PathInformation.class,System.class})

Hope this helps.let me know if it doesn't work

回答6:

System class is declared as final and cannot be mocked by libraries such as PowerMock. Several answers posted here are incorrect. If you are using Apache System Utils you can use getEnvironmentVariable method instead of calling System.getenv directly. SystemUtils can be mocked since it is not declared as final.