Static Block

 Problem

我想測試getWindowsMajorVersion method，但由於使用了static block導致我無法同時測到在Windows與Linux的情況:

public class PlatformUtil {
	private final static String mOSName = System.getProperty("os.name"); 
	private final static boolean IS_WINDOWS;
 
	static {
		IS_WINDOWS = mOSName.toUpperCase().indexOf("WINDOWS") != -1;
	}
 
	public static boolean isWindows(){
		return IS_WINDOWS;
	}
 
	public static int getWindowsMajorVersion(){
		if( !isWindows() ){
			return -1;
		}
 
		String osVersion = System.getProperty("os.version");
		int dotIndex = osVersion.indexOf(".");
		String majorVersionStr = osVersion;
		if( dotIndex != -1 ){
			majorVersionStr = osVersion.substring(0, dotIndex);
		}
		try {
			return Integer.valueOf(majorVersionStr);
		} catch( NumberFormatException e ){
			return -1;
		}
	}
}

Solution

Suppress static initializer

Powermock提供@SuppressStaticInitializationFor的annotation讓你可以skip static init。加上這個annotation，接著在testcase中去mockStaticPartial isWindows method，就可以完成在Windows與Linux上的測試案例:

@RunWith(PowerMockRunner.class)
@PrepareForTest({PlatformUtil.class, System.class})
@SuppressStaticInitializationFor("org.tonylin.practice.powermock.PlatformUtil")
public class TestPlatformUtil
 
	private void mockIsWindowsResult(boolean aResult){
		PowerMock.reset(PlatformUtil.class);
		PowerMock.mockStaticPartial(PlatformUtil.class, "isWindows");
		PlatformUtil.isWindows();
		PowerMock.expectLastCall().andReturn(aResult).anyTimes();
		PowerMock.replay(PlatformUtil.class);
	}
 
	@Test
	public void getWindowsMajorVersion(){
		PowerMock.mockStatic(System.class);
 
		// mock the os is windows.
		mockIsWindowsResult(true);
 
		mockWindowsProperties("Windows XP", "5.1.2600");
		assertEquals( 5, PlatformUtil.getWindowsMajorVersion());
		mockWindowsProperties("Windows 7", "");
		assertEquals( -1, PlatformUtil.getWindowsMajorVersion());
		mockWindowsProperties("Windows 7", "ss");
		assertEquals( -1, PlatformUtil.getWindowsMajorVersion());
 
		// mock the os is linux.
		mockIsWindowsResult(false);
 
		mockWindowsProperties("Linux", "6.1");
		assertEquals( -1, PlatformUtil.getWindowsMajorVersion());
	}
}