Mockito.inOrder() Example

1. Introduction

Mockito's InOrder is a powerful tool used to verify the order of interactions with mocks. Ensuring the correct sequence of method calls can be crucial in some scenarios, especially when the order of operations affects the outcome of the process. With InOrder, we can specify the exact sequence in which we expect interactions to happen on our mock.

2. Example Steps

1. Define an interface representing a simple task service.

2. Implement the interface with a concrete class.

3. Set up a test class for the service.

4. Mock the interface using Mockito.

5. Execute methods on the mock to simulate various tasks.

6. Use InOrder to verify the sequence of the method calls.

3. Mockito.inOrder() Example

import org.junit.jupiter.api.Test;
import org.mockito.InOrder;
import static org.mockito.Mockito.*;

// Step 1: Define an interface
interface TaskService {
    void taskOne();
    void taskTwo();
}

// Step 2: Implement the interface
class SimpleTaskService implements TaskService {
    @Override
    public void taskOne() {
        // Task One implementation here
    }

    @Override
    public void taskTwo() {
        // Task Two implementation here
    }
}

public class TaskServiceTest {

    @Test
    public void testMethodOrderWithInOrder() {
        // Step 4: Mock the TaskService interface
        TaskService mockedService = mock(TaskService.class);

        // Step 5: Call methods on the mock
        mockedService.taskOne();
        mockedService.taskTwo();

        // Step 6: Verify the order of method calls using InOrder
        InOrder inOrder = inOrder(mockedService);
        inOrder.verify(mockedService).taskOne();
        inOrder.verify(mockedService).taskTwo();
    }
}

Output:

The test will pass successfully, confirming that methods on the mockedService mock were called in the specified order: first taskOne(), then taskTwo().

4. Step By Step Explanation

1. We start by defining a TaskService interface with two methods, simulating simple tasks.

2. SimpleTaskService provides a concrete implementation for these tasks, although the actual implementation details aren't relevant for this example.

3. In the TaskServiceTest class, we set up our mock of the TaskService interface.

4. We then simulate some operations by calling taskOne() followed by taskTwo() on the mock.

5. Using Mockito's InOrder, we verify the sequence of method calls. We create an InOrder instance specifying our mock and then verify the interactions in the order we expect.

6. If we had mixed up the sequence, or missed verifying an interaction, the test would fail, ensuring that the specified order of operations is maintained.