Mocking private methods directly using reflection in Java is not possible. Reflection allows access to public and protected members, but not private ones.
However, you can achieve similar behavior by:
- Refactoring: The most recommended approach is to refactor the code to make the private method accessible. You can achieve this by:
- Making the method package-private: This makes the method accessible only within the same package.
- Creating a public wrapper method: This method calls the private method internally and allows for controlled access.
- Using PowerMock: PowerMock is a powerful mocking framework that extends Mockito and allows mocking private methods. It uses bytecode manipulation to achieve this.
Here are some examples:
Refactoring:
// Original code
class MyClass {
private void privateMethod() {
// ...
}
}
// Refactored code
class MyClass {
void publicWrapperMethod() {
privateMethod();
}
private void privateMethod() {
// ...
}
}
Using PowerMock:
@RunWith(PowerMockRunner.class)
@PrepareForTest(MyClass.class)
public class MyClassTest {
@Test
public void testPrivateMethod() throws Exception {
// Mock the private method
PowerMockito.mockStatic(MyClass.class);
PowerMockito.when(MyClass.privateMethod()).thenReturn("mocked value");
// Call the method that uses the private method
MyClass myClass = new MyClass();
String result = myClass.publicMethod();
// Assert the result
assertEquals("mocked value", result);
}
}
Remember that mocking private methods can be challenging and might lead to code that is difficult to maintain and test. Refactoring to make methods accessible is generally the preferred approach.