Mockito's Verify Method

Mockito's verify method is a powerful tool when it comes to unit testing in Java. It allows you to confirm that a certain method was called with specific arguments during the execution of a test. In this guide, we'll dive into the details of how to use the verify method effectively.

Basic Usage

The most basic usage of verify is to simply confirm that a method was called during the execution of a test. Here's an example:

// create mock object
List<String> list = Mockito.mock(List.class);

// call method under test
list.add("hello");

// verify that add was called exactly once
Mockito.verify(list).add("hello");

In this example, we create a mock object of the List class and call its add method with the argument "hello". We then use verify to confirm that the add method was called exactly once with the argument "hello".

Multiple Calls

If a method is called multiple times during the execution of a test, you can use the times argument of verify to specify how many times it should have been called. Here's an example:

// create mock object
List<String> list = Mockito.mock(List.class);

// call method under test
list.add("hello");
list.add("world");

// verify that add was called twice
Mockito.verify(list, Mockito.times(2)).add(Mockito.anyString());

In this example, we call the add method twice with different arguments. We use verify with the times argument set to 2 to confirm that the add method was called exactly twice. We also use Mockito.anyString() as the argument for add since we don't care about the specific string values.

Argument Matchers

Using Mockito.any*() argument matchers allows you to verify that a method was called with any value of a certain type. Here's an example:

// create mock object
List<String> list = Mockito.mock(List.class);

// call method under test
list.add("hello");
list.add("world");

// verify that add was called with any String twice
Mockito.verify(list, Mockito.times(2)).add(Mockito.anyString());

In this example, we use Mockito.anyString() to match any String argument passed to the add method. This allows us to verify that the method was called with any String argument twice.

Conclusion

In this guide, we covered the basics of using Mockito's verify method. With this powerful tool, you can easily confirm that certain methods were called with specific arguments during the execution of a test. By using times arguments and argument matchers, you can make your verifications more precise and increase your unit testing confidence.