ScalaTest + EasyMock

The ScalaTest + EasyMock integration library makes it fun and easy to use EasyMock with ScalaTest. To use ScalaTest + EasyMock, please add the following to your SBT project dependency:

libraryDependencies += "org.scalatestplus" %% "easymock-5-3" % "3.2.19.0" % "test"

For maven you can use:

<dependency>
    <groupId>org.scalatestplus</groupId>
    <artifactId>easymock-5-3_3</artifactId>
    <version>3.2.19.0</version>
    <scope>test</scope>
</dependency>    

ScalaTest's EasyMockSugar trait provides some basic syntax sugar for EasyMock.

Using the EasyMock API directly, you create a mock with:

val mockCollaborator = createMock(classOf[Collaborator])

With this trait, you can shorten that to:

val mockCollaborator = mock[Collaborator]

After creating mocks, you set expectations on them, using syntax like this:

mockCollaborator.documentAdded("Document")
mockCollaborator.documentChanged("Document")
expectLastCall().times(3)

If you wish to highlight which statements are setting expectations on the mock (versus which ones are actually using the mock), you can place them in an expecting clause, provided by this trait, like this:

expecting {
  mockCollaborator.documentAdded("Document")
  mockCollaborator.documentChanged("Document")
  lastCall.times(3)
}

Using an expecting clause is optional, because it does nothing but visually indicate which statements are setting expectations on mocks. (Note: this trait also provides the lastCall method, which just calls expectLastCall.)

Once you've set expectations on the mock objects, you must invoke replay on the mocks to indicate you are done setting expectations, and will start using the mock. After using the mock, you must invoke verify to check to make sure the mock was used in accordance with the expectations you set on it. Here's how that looks when you use the EasyMock API directly:

replay(mockCollaborator)
classUnderTest.addDocument("Document", new Array[Byte](0))
classUnderTest.addDocument("Document", new Array[Byte](0))
classUnderTest.addDocument("Document", new Array[Byte](0))
classUnderTest.addDocument("Document", new Array[Byte](0))
verify(mockCollaborator)

This trait enables you to use the following, more declarative syntax instead:

whenExecuting(mockCollaborator) {
  classUnderTest.addDocument("Document", new Array[Byte](0))
  classUnderTest.addDocument("Document", new Array[Byte](0))
  classUnderTest.addDocument("Document", new Array[Byte](0))
  classUnderTest.addDocument("Document", new Array[Byte](0))
}

The whenExecuting method will pass the mockCollaborator to replay, execute the passed function (your code that uses the mock), and call verify, passing in the mockCollaborator. If you want to use multiple mocks, you can pass multiple mocks to whenExecuting.

To summarize, here's what a typical test using EasyMockSugar looks like:

val mockCollaborator = mock[Collaborator]

expecting {
  mockCollaborator.documentAdded("Document")
  mockCollaborator.documentChanged("Document")
  lastCall.times(3)
}

whenExecuting(mockCollaborator) {
  classUnderTest.addDocument("Document", new Array[Byte](0))
  classUnderTest.addDocument("Document", new Array[Byte](0))
  classUnderTest.addDocument("Document", new Array[Byte](0))
  classUnderTest.addDocument("Document", new Array[Byte](0))
}

An alternative approach is to place your mock objects in a MockObjects holder object referenced from an implicit val, then use the overloaded variant of whenExecuting that takes an implicit MockObjects parameter. Here's how that would look:

implicit val mocks = MockObjects(mock[Collaborator])

expecting {
  mockCollaborator.documentAdded("Document")
  mockCollaborator.documentChanged("Document")
  lastCall.times(3)
}

whenExecuting {
  classUnderTest.addDocument("Document", new Array[Byte](0))
  classUnderTest.addDocument("Document", new Array[Byte](0))
  classUnderTest.addDocument("Document", new Array[Byte](0))
  classUnderTest.addDocument("Document", new Array[Byte](0))
}