What s the best mock framework for Java

Question

What s the best framework for creating mock objects in Java  Why  What are the pros and cons of each framework

User · Answer

Yes  Mockito is a great framework  I use it together with hamcrest and Google guice to setup my tests

User · Answer

We are heavily using EasyMock and EasyMock Class Extension at work and are pretty happy with it  It basically gives you everything you need  Take a look at the documentation  there s a very nice example which shows you all the features of EasyMock

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I am the creator of PowerMock so obviously I must recommend that   -   PowerMock extends both EasyMock and Mockito with the ability to mock static methods  final and even private methods  The EasyMock support is complete  but the Mockito plugin needs some more work  We are planning to add JMock support as well    PowerMock is not intended to replace other frameworks  rather it can be used in the tricky situations when other frameworks does t allow mocking  PowerMock also contains other useful features such as suppressing static initializers and constructors

User · Answer

I started using mocks with EasyMock  Easy enough to understand  but the replay step was kinda annoying  Mockito removes this  also has a cleaner syntax as it looks like readability was one of its primary goals  I cannot stress enough how important this is  since most of developers will spend their time reading and maintaining existing code  not creating it    Another nice thing is that interfaces and implementation classes are handled in the same way  unlike in EasyMock where still you need to remember  and check  to use an EasyMock Class Extension   I ve taken a quick look at JMockit recently  and while the laundry list of features is pretty comprehensive  I think the price of this is legibility of resulting code  and having to write more    For me  Mockito hits the sweet spot  being easy to write and read  and dealing with majority of the situations most code will require  Using Mockito with PowerMock would be my choice   One thing to consider is that the tool you would choose if you were developing by yourself  or in a small tight-knit team  might not be the best to get for a large company with developers of varying skill levels  Readability  ease of use and simplicity would need more consideration in the latter case  No sense in getting the ultimate mocking framework if a lot of people end up not using it or not maintaining the tests

User · Answer

Mockito also provides the option of stubbing methods  matching arguments  like anyInt   and anyString     verifying the number of invocations  times 3   atLeastOnce    never     and more   I ve also found that Mockito is simple and clean   One thing I don t like about Mockito is that you can t stub static methods

User · Answer

I like JMock because you are able to set up expectations  This is totally different from checking if a method was called found in some mock libraries  Using JMock you can write very sophisticated expectations  See the jmock cheat-sheat

User · Answer

I used JMock early  I ve tried Mockito at my last project and liked it  More concise  more cleaner  PowerMock covers all needs which are absent in Mockito  such as mocking a static code  mocking an instance creation  mocking final classes and methods  So I have all I need to perform my work

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I ve been having success with JMockit   It s pretty new  and so it s a bit raw and under-documented   It uses ASM to dynamically redefine the class bytecode  so it can mock out all methods including static  private  constructors  and static initializers   For example   import mockit Mockit       Mockit redefineMethods MyClassWithStaticInit class                         MyReplacementClass class       class MyReplacementClass     public void  init            replace default constructor   public static void  clinit         replace static initializer   public static void myStatic         replace static method      etc        It has an Expectations interface allowing record playback scenarios as well   import mockit Expectations  import org testng annotations Test   public class ExpecationsTest     private MyClass obj      Test   public void testFoo         new Expectations true          MyClass c                  obj   c          invokeReturning c getFoo  foo   false    bas                        assert  bas  equals obj getFoo  foo   false         Expectations assertSatisfied           public static class MyClass       public String getFoo String str  boolean bool          if  bool            return  foo           else           return  bar                         The downside is that it requires Java 5 6

User · Answer

For something a little different  you could use JRuby and Mocha which are combined in JtestR to write tests for your Java code in expressive and succinct Ruby  There are some useful mocking examples with JtestR here  One advantage of this approach is that mocking concrete classes is very straightforward

User · Answer

You could also have a look at testing using Groovy  In Groovy you can easily mock Java interfaces using the  as  operator   def request    isUserInRole    roleName - gt  roleName     testRole    as HttpServletRequest    Apart from this basic functionality Groovy offers a lot more on the mocking front  including the powerful MockFor and StubFor classes   http   docs codehaus org display GROOVY Groovy Mocks

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The JMockit project site contains plenty of comparative information for current mocking toolkits   In particular  check out the feature comparison matrix  which covers EasyMock  jMock  Mockito  Unitils Mock  PowerMock  and of course JMockit  I try to keep it accurate and up-to-date  as much as possible

User · Answer

I ve had good success using Mockito   When I tried learning about JMock and EasyMock  I found the learning curve to be a bit steep  though maybe that s just me    I like Mockito because of its simple and clean syntax that I was able to grasp pretty quickly  The minimal syntax is designed to support the common cases very well  although the few times I needed to do something more complicated I found what I wanted was supported and easy to grasp   Here s an  abridged  example from the Mockito homepage   import static org mockito Mockito     List mockedList   mock List class   mockedList clear    verify mockedList  clear      It doesn t get much simpler than that   The only major downside I can think of is that it won t mock static methods

User · Answer

The best solution to mocking is to have the machine do all the work with automated specification-based testing  For Java  see ScalaCheck and the Reductio framework included in the Functional Java library  With automated specification-based testing frameworks  you supply a specification of the method under test  a property about it that should be true  and the framework generates tests as well as mock objects  automatically   For example  the following property tests the Math sqrt method to see if the square root of any positive number n squared is equal to n   val propSqrt   forAll    n  Int    gt   n  gt   0     gt  scala Math sqrt n n     n     When you call propSqrt check    ScalaCheck generates hundreds of integers and checks your property for each  also automatically making sure that the edge cases are covered well   Even though ScalaCheck is written in Scala  and requires the Scala Compiler  it s easy to test Java code with it  The Reductio framework in Functional Java is a pure Java implementation of the same concepts

User · Answer

I started using mocks through JMock  but eventually transitioned to use EasyMock  EasyMock was just that  --easier-- and provided a syntax that felt more natural  I haven t switched since

[java] What's the best mock framework for Java?

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