How to verify a method of a non-mock object is called?

java

mockito

testing

dependency-injection

byNikita Barsukov·Feb 22, 2025

For capturing calls on real objects, use Mockito.spy. Create a spy of your instance, implement the method, and finally, verify the call.

YourClass realObject = new YourClass();
YourClass spy = Mockito.spy(realObject);

spy.methodToVerify();

Mockito.verify(spy).methodToVerify(); // Spy, don't pry

To test whether a method is called on a real object, spying is the goto guy. It's different from mocks; spies encapsulate real objects and delegate calls to them. This method allows you to use the real object's behavior while monitoring its interaction.

Spies: Aligning Forces with the Real Object

The @Spy annotation comes in handy to declare spies in your test:

@Spy
YourClass mySpy;

// Inside the testing method
Mockito.verify(mySpy).methodToVerify(); // Spy is the new judge in town

Here, we use the @Spy annotation, which saves us from creating a spy manually. This method proves to be fruitful in contexts like Spring, where dependency injection is supported.

Behavioral Testing: Turn the Spy Mode On

Spies jump into action when you need to perform behavioral testing on real objects. Instead of swapping functional behavior with a mock, you can assure that the class under examination interacts as expected with complex legacy code or third-party libraries.

Sinkholes Along the Way

While using spies, you might stumble upon the following issues:

Spies can lead to flaky tests if the underlying behavior isn't stable.
Overuse of spies may lead to unfocused, overly verbose tests.
Employ spies wisely in your tests. Some operations might still use real objects if spies aren't properly injected.

Spy Agencies Best Practices

Recruit spies to wrap critical dependencies, don't try to spy the entire world.
Senior spies should verify integration points to confirm if they are being utilized as expected.
Remember, dependency injection can easily give a real object a spy makeover.

explain-codes / Java / How to verify a method of a non-mock object is called?

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