Overview

Today, I’d like to share different ways to verify interactions with mock objects in Mockito via methods: verify(), verifyZeroInteractions(), verifyNoMoreInteractions(), and inOrder(). After reading this article, you will understand:

  • How to verify the exact number of invocations?
  • How to verify the boundaries of invocations (at most, at least)?
  • How to verify no more interactions with other methods?
  • How to verify the invocations are in order?

This article is written with Mockito 1.10.19 (it’s a bit old now, I know…). Without additional specification, all methods without class prefix come from factory class org.mockito.Mockito:

import static org.mockito.Mockito.*;

Verify Exact Invocations

The exact number of invocations can be asserted via method Mockito#verify(T mock, VerificationMode mode) combined with verification mode Times. You need to provide the target mock object to be verified, the expected number of calls (non-negative), and also the invocation to be verified. For example, given an instance of class “Context”, called “mockContext”, and a validator, I would like to verify that when validating input string “Hello world!”, an error is added to the context as “No space allowed”:

Context mockContext = mock(Context.class);

Validator validator = new Validator(mockContext);
validator.validate("Hello world!");

verify(mockContext, times(1)).addError("No space allowed.");

Or using alias method (times=1):

verify(mockContext).addError("No space allowed.");

Now, if you need to verify invocation happens several times, you can just modify the value of times. For example, validating three sentences, two of which contain space, then two errors will be added:

Context mockContext = mock(Context.class);

Validator validator = new Validator(mockContext);
validator.validate("Hello world!"); // error
validator.validate("Hello Java!");  // error
validator.validate("Hello!");       // ok

verify(mockContext, times(2)).addError("No space allowed.");

If you want to ensure target invocation never happens, you can set times=0 or use alias method never():

verify(mockContext, never()).addError("No space allowed.");

Verify Boundaries of Invocations

If you want to verify the target method is invoked at least or at most N times, you can use factory method Mockito.atLeast(int), Mockito.atLeastOnce(), and Mockito.atMost(int).

At least:

Context mockContext = mock(Context.class);

Validator validator = new Validator(mockContext);
validator.validate("Hello world!");
validator.validate("Hello Java!");
...

verify(mockContext, atLeast(2)).addError("No space allowed.");

At least once:

verify(mockContext, atLeastOnce()).addError("No space allowed.");

At most:

verify(mockContext, atMost(2)).addError("No space allowed.");

Verify Interaction with Other Methods

Beside verifying the invocations of the target method, you may also want to ensure that there is no more interaction with other methods. This can be done using Mockito.verifyNoMoreInteractions. For example, the following code ensures that beside addError(String), there is no more interaction with the context mockContext. Method like Context#neverCalled() is never called by validator.

Context mockContext = mock(Context.class);

Validator validator = new Validator(mockContext);
validator.validate("Hello world");

verify(mockContext).addError("No space allowed.");
verifyNoMoreInteractions(mockContext);

In other words, the only invocation is Context#addError.

verify(mockContext, only()).addError("No space allowed.");

Personally, I don’t recommend this kind of verification because it is too strict: it means that you don’t trust the actual implementation and the test needs to be updated frequently, every time when more interaction is added with the target mock object.

Verify Invocation Order

Perform in-order verifications for one or more mock objects. In this way, you can verify if one method is called before another. It also works for multiple mocks. Also, verification in-order is flexible—you don’t have to verify all interactions one-by-one but only those that you are interested in testing in order.

Here’s an example with two mock objects to be verified. Only error A and error C are asserted, error B is ignored.

Context ctx1 = mock(Context.class);
Context ctx2 = mock(Context.class);

ctx1.addError("A");
ctx2.addError("B");
ctx2.addError("C");

// all verifications done in same InOrder instance
InOrder inOrder = inOrder(ctx1, ctx2);
inOrder.verify(ctx1).addError("A");
// you don't have to verify all interactions, but only
// mocks that are relevant for in-order verification
inOrder.verify(ctx2).addError("C");

Conclusion

In this article, we saw different methods in Mockito to verify invocations with mock objects. The source code of this article is available on GitHub as MockitoVerifyTest.java. Hope you enjoy this article, see you the next time!

References