How do I verify that a mock method was called with a custom matcher

1. Creating a Custom Matcher**

First, you need to create a custom matcher that will be used to verify the arguments passed to the mock method. Mockito provides the `ArgumentMatcher` interface for this purpose. Here's an example of how you can create a custom matcher:

java
import org.mockito.ArgumentMatcher;

public class CustomMatcher extends ArgumentMatcher {
    private String expectedValue;

    public CustomMatcher(String expectedValue) {
        this.expectedValue = expectedValue;
    }

    @Override
    public boolean matches(String argument) {
        // Implement your custom logic here
        // For example, checking if the argument contains a certain substring
        return argument.contains(expectedValue);
    }

    @Override
    public String toString() {
        return "CustomMatcher{" +
                "expectedValue='" + expectedValue + '\'' +
                '}';
    }
}

2. Using the Custom Matcher in Verification**

To verify that a mock method was called with an argument that matches your custom matcher, you can use the `argThat` method provided by Mockito. Here's how you can do it:

java
import org.mockito.Mockito;

// Assuming you have a mock object named 'mockObject'
// and a method 'myMethod' that you want to verify

// Create a custom matcher instance
CustomMatcher customMatcher = new CustomMatcher("expectedSubstring");

// Verify that the method was called with an argument matching the custom matcher
verify(mockObject).myMethod(argThat(customMatcher));

In this example, `argThat` is used to pass your custom matcher to the verification method. Mockito will then check if the actual argument passed to `myMethod` matches the condition defined in your custom matcher.

3. Capturing Arguments for Further Verification**

If you need to capture the actual argument passed to the method for further verification, you can use `ArgumentCaptor`. Here's how you can combine it with a custom matcher:

java
import org.mockito.ArgumentCaptor;

// Create an ArgumentCaptor for the type of argument you're interested in
ArgumentCaptor captor = ArgumentCaptor.forClass(String.class);

// Verify that the method was called with any argument (captured for later inspection)
verify(mockObject).myMethod(captor.capture());

// Now you can inspect the captured argument(s)
String capturedArgument = captor.getValue();

// Use your custom matcher to verify the captured argument
assertTrue(new CustomMatcher("expectedSubstring").matches(capturedArgument));

This approach allows you to capture the actual argument and then apply your custom verification logic.

4. Using Verification Modes**

Mockito also supports various verification modes, such as `times`, `atLeast`, `atMost`, etc., which can be used in conjunction with custom matchers to verify not just the arguments but also the number of invocations:

java
// Verify that the method was called exactly once with the custom matcher
verify(mockObject, times(1)).myMethod(argThat(customMatcher));

Conclusion

By combining custom matchers with Mockito's verification capabilities, you can write robust tests that ensure your code behaves as expected under various conditions. Whether you're verifying specific argument values or ensuring that methods are called with certain parameters, Mockito provides the tools you need to write comprehensive unit tests.