Testing Mastery: JUnit, Mockito & Integration Tests · Aula

Verificando Interações com Mocks

Aprenda a verificar se objetos simulados foram chamados com os argumentos esperados e um número específico de vezes.

Verificando Interações com Mocks é uma aula grátis de Testing Mastery: JUnit, Mockito & Integration Tests no CoddyKit. Esta é a aula 3 de 4. Você pode ler a aula completa abaixo gratuitamente — depois pratica ao vivo no navegador com um editor de código integrado e um tutor de IA 24/7. Faz parte do caminho de aprendizado de Testing Mastery: JUnit, Mockito & Integration Tests, e seu progresso é sincronizado entre a web e o app CoddyKit. O curso de Testing Mastery: JUnit, Mockito & Integration Tests inclui 4 aulas no total.

Partes desta aula ainda não foram traduzidas e aparecem em inglês.

Intro to Mockito Verification

Welcome to verifying mock interactions! After learning to create mocks, the next crucial step is to confirm how they were used.

Verification in Mockito means checking if specific methods on your mock objects were called during a test.

Why Verify Interactions?

When testing a class, you often want to ensure it correctly interacts with its dependencies.

Collaboration Check: Did the object under test call the right methods on its collaborators?
Behavior Confirmation: Did it pass the correct arguments to those methods?
Interaction Count: Was a method called once, multiple times, or not at all?

Verification answers these questions, ensuring your code behaves as expected.

The Basic `verify()` Method

The simplest way to verify an interaction is using Mockito.verify(). It checks if a method was called exactly once.

You write verify(mockObject).methodCall(); after the code under test has run. If the method wasn't called, or was called more than once, Mockito will throw an error.

Code: Basic `verify()` in Action

Try this runnable example. We'll simulate a test by creating a mock and calling a method on it. Then, we verify the interaction.

In a real JUnit test, a failed verification would make the test fail.

import static org.mockito.Mockito.*;

interface MyService {
    void doSomething();
}

class MyProcessor {
    private MyService service;
    public MyProcessor(MyService service) {
        this.service = service;
    }
    public void execute() {
        service.doSomething();
    }
}

public class Main {
    public static void main(String[] args) {
        MyService mockService = mock(MyService.class);
        MyProcessor processor = new MyProcessor(mockService);

        System.out.println("Calling execute...");
        processor.execute(); // This calls mockService.doSomething()

        try {
            // Verify doSomething() was called exactly once
            verify(mockService).doSomething();
            System.out.println("\nVerification successful: doSomething() called once.");
        } catch (Throwable e) {
            System.out.println("\nVerification failed: " + e.getMessage());
        }
        System.out.println("Program finished.");
    }
}

Verifying Specific Arguments with `eq()`

Often, you need to check not just if a method was called, but with what arguments.

Use eq(value) to match an exact argument value. For example, verify(mock).someMethod(eq("hello"), eq(123)); ensures the method was called with "hello" and 123.

You can also use generic matchers like anyString() or anyInt() if you don't care about a specific argument's value.

Code: `verify()` with `eq()`

Here, we verify that a message was sent with specific content and priority. Notice how eq() helps us be precise.

import static org.mockito.Mockito.*;

interface DataSender {
    void send(String message, int priority);
}

class MessageProcessor {
    private DataSender sender;
    public MessageProcessor(DataSender sender) {
        this.sender = sender;
    }
    public void processAndSend(String data) {
        sender.send(data.toUpperCase(), 1);
    }
}

public class Main {
    public static void main(String[] args) {
        DataSender mockSender = mock(DataSender.class);
        MessageProcessor processor = new MessageProcessor(mockSender);

        System.out.println("Processing 'hello' message...");
        processor.processAndSend("hello");

        try {
            // Verify send() was called with "HELLO" and 1
            verify(mockSender).send(eq("HELLO"), eq(1));
            System.out.println("\nVerification successful: Correct arguments received.");
        } catch (Throwable e) {
            System.out.println("\nVerification failed: " + e.getMessage());
        }

        // The following commented block shows a failing verification
        // try {
        //     verify(mockSender).send(eq("hello"), eq(1)); // "hello" (lowercase) is wrong
        //     System.out.println("This should not be printed.");
        // } catch (Throwable e) {
        //     System.out.println("Expected failure for wrong arguments: " + e.getMessage());
        // }
        System.out.println("Program finished.");
    }
}

Verifying Call Counts: `times()` & `never()`

Sometimes, you need to verify how many times a method was called:

verify(mock, times(N)).method();: Called exactly N times.
verify(mock, never()).method();: Never called (same as times(0)).

These are powerful for ensuring loops, conditions, or error handling work correctly.

Code: `times()` and `never()`

This example processes multiple events and logs an error. We'll verify the exact number of times each type of log was made.

import static org.mockito.Mockito.*;

interface EventLogger {
    void log(String event);
}

class EventProcessor {
    private EventLogger logger;
    public EventProcessor(EventLogger logger) {
        this.logger = logger;
    }
    public void processEvents(int count) {
        for (int i = 0; i < count; i++) {
            logger.log("Event " + (i + 1));
        }
    }
    public void logError(String error) {
        logger.log("ERROR: " + error);
    }
}

public class Main {
    public static void main(String[] args) {
        EventLogger mockLogger = mock(EventLogger.class);
        EventProcessor processor = new EventProcessor(mockLogger);

        System.out.println("Processing 3 events and logging an error...");
        processor.processEvents(3);
        processor.logError("Failed to connect");

        try {
            // Verify log() was called 3 times with arguments starting with "Event "
            verify(mockLogger, times(3)).log(startsWith("Event "));
            System.out.println("\nVerification successful: 'Event' logged 3 times.");

            // Verify log() was called once with the exact error message
            verify(mockLogger, times(1)).log(eq("ERROR: Failed to connect"));
            System.out.println("Verification successful: Error logged once.");

            // Verify log() was never called with arguments starting with "WARNING"
            verify(mockLogger, never()).log(startsWith("WARNING"));
            System.out.println("Verification successful: 'WARNING' never logged.");

        } catch (Throwable e) {
            System.out.println("\nVerification failed: " + e.getMessage());
        }
        System.out.println("Program finished.");
    }
}

Flexible Call Counts: `atLeast()`, `atMost()`

Sometimes an exact count isn't necessary, but a range is important:

verify(mock, atLeast(N)).method();: Called N or more times.
verify(mock, atMost(N)).method();: Called N or fewer times.

There are also convenient shortcuts: atLeastOnce() and atMostOnce() for clarity.

Verify Interactions Check

Which of the following are valid ways to verify method calls using Mockito?

Recap: Mastering Verification

You've learned how to verify mock interactions in Mockito!

verify(mock).method(); checks for a single call.
Use eq() for exact argument matching or generic matchers like anyString().
Control call counts with times(N), never(), atLeast(N), and atMost(N).

Mastering verification is key to writing robust, reliable unit tests that confirm precise object collaboration.

Perguntas Frequentes

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Aprenda a verificar se objetos simulados foram chamados com os argumentos esperados e um número específico de vezes. Você pratica Testing Mastery: JUnit, Mockito & Integration Tests com código prático que executa diretamente no navegador, e um tutor de IA 24/7 responde suas dúvidas enquanto trabalha na aula.

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Todas as aulas deste curso

Mocks, Stubs e Fakes
Criando Mocks com Mockito
Verificando Interações com Mocks
Injetando objetos simulados com @Mock e @InjectMocks

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