Mockito Verify Cookbook

1. Overview

This cookbook illustrates how to use Mockito verify in a variety of use cases.

The format of the cookbook is example-focused and practical — no extraneous details and explanations are necessary.

We're going to be mocking a simple list implementation:

public class MyList extends AbstractList<String> {

    @Override
    public String get(final int index) {
        return null;
    }
    
    @Override
    public int size() {
        return 1;
    }
}

2. The Cookbook

Verify simple invocation on mock:

List<String> mockedList = mock(MyList.class);
mockedList.size();

verify(mockedList).size();

Verify the number of interactions with mock:

List<String> mockedList = mock(MyList.class);
mockedList.size();
verify(mockedList, times(1)).size();

Verify no interaction with the whole mock occurred:

List<String> mockedList = mock(MyList.class);
verifyNoInteractions(mockedList);

Verify no interaction with a specific method occurred:

List<String> mockedList = mock(MyList.class);
verify(mockedList, times(0)).size();

Verify there are no unexpected interactions — this should fail:

List<String> mockedList = mock(MyList.class);
mockedList.size();
mockedList.clear();

verify(mockedList).size();
assertThrows(NoInteractionsWanted.class, () -> verifyNoMoreInteractions(mockedList));

Verify the order of interactions:

List<String> mockedList = mock(MyList.class);
mockedList.size();
mockedList.add("a parameter");
mockedList.clear();

InOrder inOrder = Mockito.inOrder(mockedList);
inOrder.verify(mockedList).size();
inOrder.verify(mockedList).add("a parameter");
inOrder.verify(mockedList).clear();

Verify an interaction has not occurred:

List<String> mockedList = mock(MyList.class);
mockedList.size();

verify(mockedList, never()).clear();

Verify an interaction has occurred at least a certain number of times:

List<String> mockedList = mock(MyList.class);
mockedList.clear();
mockedList.clear();
mockedList.clear();

verify(mockedList, atLeast(1)).clear();
verify(mockedList, atMost(10)).clear();

Verify interaction with the exact argument:

List<String> mockedList = mock(MyList.class);
mockedList.add("test");

verify(mockedList).add("test");

Verify interaction with flexible/any argument:

List<String> mockedList = mock(MyList.class);
mockedList.add("test");

verify(mockedList).add(anyString());

Verify interaction using argument capture:

List<String> mockedList = mock(MyList.class);
mockedList.addAll(Lists.<String> newArrayList("someElement"));

ArgumentCaptor<List<String>> argumentCaptor = ArgumentCaptor.forClass(List.class);
verify(mockedList).addAll(argumentCaptor.capture());

List<String> capturedArgument = argumentCaptor.getValue();
assertThat(capturedArgument).contains("someElement");

3. Conclusion

The goal of this guide is to have this information readily available online. I've published a few similar development cookbooks on Google Guava and Hamcrest.

The implementation of all these examples and code snippets can be found on GitHub. This is a Maven-based project, so it should be easy to import and run as it is.

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