Java – Mocking non-public static methods in abstract classes with JMockit

javajmockitmockingunit testing

I have the following class:

public abstract class AbstractParent {
    static String method() {
        return "OriginalOutput";
    }
}

I want to mock this method. I decide to use JMockit. So I create a mock class:

public class MockParent {
    static String method() {
        return "MOCK";
    }
}

And my test code looks like this:

public class RealParentTest {

    @Before
    public void setUp() throws Exception {
        Mockit.redefineMethods( AbstractParent.class, MockParent.class );
    }


    @Test
    public void testMethod() {
        assertEquals(MockParent.method(),AbstractParent.method());
    }

}

Unfortunately this test says that AbstractParent returns "OriginalOutput" instead of "MOCK". Any ideas why? Am I doing something wrong? I've tried declaring my mock class as abstract as well, to no avail.

Edit Note that making the method public causes the test to run without a problem… this is weird because with JMockit you are supposed to be able to mock methods of any scope.

Answer Only the mock method needs to be public, you can leave the original method as is.

Best Answer

Found the solution: you simply need to make the mock's method public (the original method can stay in its original visibility).

I don't know why this works while the original way doesn't (someone who does is more than welcome to chime in), but all you need to do is simply change the mock class in the example above to:

public class MockParent {
    public static String method() {
        return "MOCK";
    }
}

Related Solutions

Java – How to test a class that has private methods, fields or inner classes

Update:

Some 10 years later perhaps the best way to test a private method, or any inaccessible member, is via @Jailbreak from the Manifold framework.
@Jailbreak Foo foo = new Foo();
// Direct, *type-safe* access to *all* foo's members
foo.privateMethod(x, y, z);
foo.privateField = value;
This way your code remains type-safe and readable. No design compromises, no overexposing methods and fields for the sake of tests.

If you have somewhat of a legacy Java application, and you're not allowed to change the visibility of your methods, the best way to test private methods is to use reflection.

Internally we're using helpers to get/set private and private static variables as well as invoke private and private static methods. The following patterns will let you do pretty much anything related to the private methods and fields. Of course, you can't change private static final variables through reflection.

Method method = TargetClass.getDeclaredMethod(methodName, argClasses);
method.setAccessible(true);
return method.invoke(targetObject, argObjects);

And for fields:

Field field = TargetClass.getDeclaredField(fieldName);
field.setAccessible(true);
field.set(object, value);

Notes:
1. TargetClass.getDeclaredMethod(methodName, argClasses) lets you look into private methods. The same thing applies for getDeclaredField.
2. The setAccessible(true) is required to play around with privates.

Php – Best practices to test protected methods with PHPUnit

If you're using PHP5 (>= 5.3.2) with PHPUnit, you can test your private and protected methods by using reflection to set them to be public prior to running your tests:

protected static function getMethod($name) {
  $class = new ReflectionClass('MyClass');
  $method = $class->getMethod($name);
  $method->setAccessible(true);
  return $method;
}

public function testFoo() {
  $foo = self::getMethod('foo');
  $obj = new MyClass();
  $foo->invokeArgs($obj, array(...));
  ...
}

Best Answer

Related Solutions

Java – How to test a class that has private methods, fields or inner classes

Php – Best practices to test protected methods with PHPUnit

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