How do I handle complex objects with nested properties in ArgumentMatchers

1. Using `ArgumentCaptor`**

One effective way to handle nested properties is by using `ArgumentCaptor`. This allows you to capture the argument passed to a method and then assert its properties, including nested ones.

java
// Example: Capturing and asserting nested properties
ArgumentCaptor argument = ArgumentCaptor.forClass(User.class);
verify(userService).getLastLogin(argument.capture());

User capturedUser = argument.getValue();
assertEquals("John", capturedUser.getName());
assertEquals("Doe", capturedUser.getLastName());
assertEquals("Main St", capturedUser.getAddress().getStreet());

2. Implementing Custom `ArgumentMatcher`**

If you need more control over matching, you can implement a custom `ArgumentMatcher`. This allows you to define specific conditions for matching, including nested properties.

java
// Example: Custom ArgumentMatcher for nested properties
class UserMatcher implements ArgumentMatcher {
    @Override
    public boolean matches(User user) {
        return user.getName().equals("John") && user.getAddress().getStreet().equals("Main St");
    }

    @Override
    public String toString() {
        return "User with name John and street Main St";
    }
}

// Usage
doReturn(time).when(userService).getLastLogin(argThat(new UserMatcher()));

3. Using `refEq` with Exclusions**

If you want to match an object based on reference equality but exclude certain nested fields, you can use `refEq` with exclusions. However, `refEq` does not support excluding nested fields directly (e.g., `address.city`). Instead, you can exclude top-level fields and then assert nested properties separately.

java
// Example: Excluding a top-level field
doReturn(time).when(userService).getLastLogin(ArgumentMatchers.refEq(user, "address"));

For more complex exclusions, you might need to use a combination of `ArgumentCaptor` and custom assertions.

4. Mock Openly, Assert Specifically**

A recommended strategy is to mock methods openly using `any()` and then assert specific properties using `verify()` and `ArgumentCaptor`. This approach keeps your mocking simple while allowing detailed assertions.

java
// Example: Mocking openly and asserting specifically
doReturn(time).when(userService).getLastLogin(any(User.class));

verify(userService).getLastLogin(argument.capture());
// Assert captured argument's properties

Conclusion

Handling complex objects with nested properties in Mockito involves using tools like `ArgumentCaptor`, custom `ArgumentMatcher`, and strategic mocking. While Mockito does not directly support nested matchers, these approaches provide flexible ways to manage and assert nested properties effectively.