Unable to Mock a Private Method in a Class for Unit Testing in Java using Mockito
I tried several approaches but none seem to work. I recently switched to I just started working with I'm currently facing a challenge while trying to unit test a class that has a private method which is crucial for its functionality. The class in question is a service class that processes user input and formats it before sending it to another service. I'm using Mockito for mocking dependencies and JUnit 5 for testing. Here’s a simplified version of the class I’m dealing with: ```java public class UserService { private final UserRepository userRepository; public UserService(UserRepository userRepository) { this.userRepository = userRepository; } public String processUserInput(String input) { String formattedInput = formatInput(input); return userRepository.save(formattedInput); } private String formatInput(String input) { // Imagine complex formatting logic here return input.trim().toLowerCase(); } } ``` In my unit test, I want to verify that the `formatInput` method is called with the correct parameters, but since it's private, Mockito doesn’t allow me to mock it directly. I tried to extract the formatting logic into a separate utility class, but I still want to keep the original design intact for the time being. Here’s what my unit test looks like: ```java import static org.mockito.Mockito.*; import static org.junit.jupiter.api.Assertions.*; import org.junit.jupiter.api.BeforeEach; import org.junit.jupiter.api.Test; class UserServiceTest { private UserRepository userRepository; private UserService userService; @BeforeEach void setUp() { userRepository = mock(UserRepository.class); userService = new UserService(userRepository); } @Test void testProcessUserInput() { String input = " TestInput "; when(userRepository.save(anyString())).thenReturn("Saved"); String result = userService.processUserInput(input); assertEquals("Saved", result); // Here, I wanted to assert that formatInput was called, but it's private! } } ``` I’m getting a bit stuck on how to verify the behavior of the private method without changing the architecture too much. Is there a recommended approach to handle this in Mockito, or should I consider refactoring my design to make the method more testable? I’ve looked at using PowerMockito, but I’d like to avoid that if possible due to its complexity. Any guidance would be appreciated! I've been using Java for about a year now. I've been using Java for about a year now. Cheers for any assistance! I'd be grateful for any help.