An expressive Mock Object library for Test Driven Development
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olibye Merge pull request #107 from olibye/master
Blocking alternative to non-blocking CopyOnWriteArrayList expectation strategy
Latest commit 498d09a May 23, 2018

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Recent Changes


  • Dropped JDK 6 compliance.
  • Exposed the InvocationDispatcher so that ThreadingPolicies

Upgrading to 2.8.X

Are you seeing NPEs?

We have had to make a breaking change to with(). Tests using with(any(matcher)) for method signatures that require native types will throw NullPointerException.

You should change


to the following


This is due to a compiler change in Java 1.7. The 2.6.0 release was compiled with Java 1.6 so it did not suffer this problem.

Advantages of jMock 2 over jMock 1

  • Uses real method calls, not strings, so you can refactor more easily and autocomplete in the IDE.
  • Customisation by delegation, not by inheritance.
  • Many more plugin-points for customisation.
  • Independent of any testing framework: compatability with the testing framework is a plugin-point.
  • Can mock concrete classes without calling their constructors (if you really want to).
  • Uses Hamcrest matchers, so can use a large and ever-growing library of matchers in expectations.
  • Expectations match in first-in, first-out order, so tests are easier to understand.

How to get up and running

Automatic Dependency Management

If you're using Gradle or Maven (and perhaps Ant), then it suffices to add to your build file the "integration JAR" for the test library that you want to use. For example: jmock-junit4-2.8.2.

For example, with Gradle:


Hand-Rolled Dependencies

Add the jmock-<version>.jar to your classpath. (For example: jmock-2.8.2.jar.) Also add the integration JAR to your classpath for the test library ou're using. (For example: jmock-junit4-2.8.2.jar.) You also need hamcrest-api-<version>.jar and hamcrest-lib-<version>.jar.

Package Structure

jMock 2 is organised into published and internal packages. We guarantee backwards compatability of types in published packages within the same major version of jMock. There are no guarantees about backward compatability for types in internal packages.

Types defined in published packages may themselves define public methods that accept or return types from internal packages or inherit methods from types in internal packages. Such methods have no compatability guarantees and should not be considered as part of the published interface.

Published packages


DSL-style API



Convenient classes that implement the APIs in the core, are used by the DSL-style API, and can be used in user-defined APIs


Classes integrating jMock with different testing APIs, such as JUnit 3.x, JUnit 4.x and TestNG.

Packages of example code


Lib classes that rely on clever hacks or otherwise cannot be guaranteed to always work in all JVMs. There are no compatability guarantees with these classes. Use at your own risk.

Internal packages


Internal implementation details


Tests for jMock itself

Plug-in Points


Controls the matching of invocations to expectations


Performs an action in response to an invocation


Wraps mock objects in an adapter of the correct type


Matches an invocation and fakes its behaviour


Translates expectation errors into error type used by a specific testing framework.


Creates names for mock objects based on the mocked type.


If you'd like to contribute, then do the following:

  1. clone this repository (git clone …)
  2. install Maven (brew install mvn on Mac OS, for example)
  3. $ mvn package in order to generate a signed JAR. This will run all the tests. ($ mvn test appears not to suffice.)