ScalaMock, Unexpected call: when sharing mock instance between tests

Question

I am using Scala 2.10 with ScalaMock 3.6.

I have a quite simple test case with 4 test scenarios. I have created a mock object for those tests to use (imitating file system):

class ProcessingOperatorTest extends FlatSpec with Matchers with BeforeAndAfterEach with MockFactory {
...

val fakeFS = mock[FileIO]
(fakeFS.createFile _).expects(*).returns(true).anyNumberOfTimes()
(fakeFS.exist _).expects(where { (p: String) => p.contains(existing) }).returns(true).anyNumberOfTimes()
(fakeFS.exist _).expects(where { (p: String) => p.contains(notExisting) }).returns(false).anyNumberOfTimes()

behavior of "Something"
it should "test 1" in {
   ...
}

it should "test 2" in {
   ...
}

it should "test 3" in {
   ...
}

it should "test 4" in {
   ...
}

Now:

• 1st test does not use any of mocked methods (but needs the mock object)
• 2nd test uses only existing mock method
• 3rd test uses both existing and not existing mock methods
• 4th test uses all methods, (also createFile)

Now, for some reason, when running all those tests together, 4th test fails giving me the following error. If running separately, it will pass.

Unexpected call: <mock-1> FileIO.exist(notExisting)

Expected:
inAnyOrder {

}

Actual:
  <mock-1> FileIO.exist(notExisting)
ScalaTestFailureLocation: scala.Option at (Option.scala:120)
org.scalatest.exceptions.TestFailedException: Unexpected call: <mock-1> FileIO.exist(notExisting)

...

The other walkaround is to copy-paste the mock declaration and its behaviour inside 4th it should { ... } test scenario. Tests work then (separately, and all together).

Why is global mock instance failing? I can try to prepare a similar test scenario as separate sbt project if needed.

Answer 1

Mix in org.scalatest.OneInstancePerTest as described here:

class ProcessingOperatorTest extends FlatSpec
                             with Matchers
                             with BeforeAndAfterEach
                             with MockFactory
                             with OneInstancePerTest {
  ...
}