This blog takes a look at PowerMock's ability to mock static methods, providing an example of mocking the JDK’s ResourceBundle class, which as many of you know uses ResourceBundle.getBundle(...) to, well... load resource bundles.
I, like many other bloggers and writers, usually present some highly contrived scenario to highlight the problem. Today is different, I’ve simply got a class that uses a ResourceBundle called: UsesResourceBundle:
public class UsesResourceBundle {
private static Logger logger = LoggerFactory.getLogger(UsesResourceBundle.class);
private ResourceBundle bundle;
public String getResourceString(String key) {
if (isNull(bundle)) {
// Lazy load of the resource bundle
Locale locale = getLocale();
if (isNotNull(locale)) {
this.bundle = ResourceBundle.getBundle("SomeBundleName", locale);
} else {
handleError();
}
}
return bundle.getString(key);
}
private boolean isNull(Object obj) {
return obj == null;
}
private Locale getLocale() {
return Locale.ENGLISH;
}
private boolean isNotNull(Object obj) {
return obj != null;
}
private void handleError() {
String msg = "Failed to retrieve the locale for this page";
logger.error(msg);
throw new RuntimeException(msg);
}
}
You can see that there’s one method: getResourceString(...), which given a key will retrieve a resource string from a bundle. In order to make this work a little more efficiently, I’ve lazily loaded my resource bundle, and once loaded, I call bundle.getString(key) to retrieve my resource. To test this I’ve written a PowerMock JUnit test:
import static org.easymock.EasyMock.expect;
import static org.junit.Assert.assertEquals;
import static org.powermock.api.easymock.PowerMock.mockStatic;
import static org.powermock.api.easymock.PowerMock.replayAll;
import static org.powermock.api.easymock.PowerMock.verifyAll;
import java.util.Locale;
import java.util.MissingResourceException;
import java.util.ResourceBundle;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.powermock.api.easymock.annotation.Mock;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;
@RunWith(PowerMockRunner.class)
@PrepareForTest(UsesResourceBundle.class)
public class UsesResourceBundleTest {
@Mock
private ResourceBundle bundle;
private UsesResourceBundle instance;
@Before
public void setUp() {
instance = new UsesResourceBundle();
}
@Test
public final void testGetResourceStringAndSucceed() {
mockStatic(ResourceBundle.class);
expect(ResourceBundle.getBundle("SomeBundleName", Locale.ENGLISH)).andReturn(bundle);
final String key = "DUMMY";
final String message = "This is a Message";
expect(bundle.getString(key)).andReturn(message);
replayAll();
String result = instance.getResourceString(key);
verifyAll();
assertEquals(message, result);
}
@Test(expected = MissingResourceException.class)
public final void testGetResourceStringWithStringMissing() {
mockStatic(ResourceBundle.class);
expect(ResourceBundle.getBundle("SomeBundleName", Locale.ENGLISH)).andReturn(bundle);
final String key = "DUMMY";
Exception e = new MissingResourceException(key, key, key);
expect(bundle.getString(key)).andThrow(e);
replayAll();
instance.getResourceString(key);
}
@Test(expected = MissingResourceException.class)
public final void testGetResourceStringWithBundleMissing() {
mockStatic(ResourceBundle.class);
final String key = "DUMMY";
Exception e = new MissingResourceException(key, key, key);
expect(ResourceBundle.getBundle("SomeBundleName", Locale.ENGLISH)).andThrow(e);
replayAll();
instance.getResourceString(key);
}
}
In the code above I’ve taken the unusual step of including the import statements. This is to highlight that we’re using PowerMock’s versions of the import statics and not EasyMock’s. If you accidentally import EasyMock’s statics, then the whole thing just won’t work.
There are four easy steps in setting up a test that mocks a static call:
- Use the PowerMock JUnit runner:
@RunWith(PowerMockRunner.class)
- Declare the test class that we’re mocking:
@PrepareForTest(UsesResourceBundle.class)
- Tell PowerMock the name of the class that contains static methods:
mockStatic(ResourceBundle.class);
- Setup the expectations, telling PowerMock to expect a call to a static method:
expect(ResourceBundle.getBundle("SomeBundleName", Locale.ENGLISH)).andReturn(bundle);
The rest is plain sailing, you set up expectations for other standard method calls and the tell PowerMock/EasyMock to run the test, verifying the results:
final String key = "DUMMY";
final String message = "This is a Message";
expect(bundle.getString(key)).andReturn(message);
replayAll();
String result = instance.getResourceString(key);
verifyAll();
PowerMock can do lots more, such as mocking constructors and private method calls. More on that later perhaps...
3 comments:
Hi Roger,
What about code coverage? When I add my class to @PrepareForTest, the coverage is ignored....
I'm running JUnits for code coverage purpose, can you help me with this?
Thanks in advance!
Diana,
I'm not sure what the answer to your problem is, but I'd hazard a guess that changing from the default JUnit test runner to the PowerMockRunner using:
@RunWith(PowerMockRunner.class)
will be the cause of the problems. As they say on the Powermock website "PowerMock uses a custom classloader and byte code manipulation" - which means that when you then add:
@PrepareForTest(UsesResourceBundle.class)
it'll tell PowerMock to starting doing some jiggery-pokery with your code that will confuse whatever code coverage method you're using.
I realize it's 3 years later but I use eCobertura and EclEmma for eclipse.
eCobertura for most tests and EclEmma when I want coverage on something that eCobertura can't handle.
Note: I have to use the JVM arg -XX:-UseSplitVerifier for my unit tests or I get errors, also I have to add to the plug-ins dir an older version of junit to get one of the above coverage tools to install in eclipse.
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