Question

I’ve come across a problem when mocking methods that have view bounds on the type of their parameters using Mockito and Specs2. Simply put, since a view bound translates to an extra implicit argument to the method, Mockito cannot reconcile the call described by an expectation to the actual arguments the mock recieves:

For example:

//Receiver.scala
class Receiver {
  def methodWithViewBound[T <% WrappedString](w : T) : Unit = {
    //noop!
  }
}

//WrappedString.scala
class WrappedString(val wrapped : String) {

}

//TestMockedMethodWithViewBound.scala
import org.specs2.mutable._
import org.specs2.specification._
import org.specs2.mock._
import org.mockito.Matchers

class TestMockedMethodWithViewBound extends Specification with Mockito {

  implicit def wrapString(s : String) : WrappedString = new WrappedString(s);
  implicit def unwrapString(w : WrappedString) : String = w.wrapped;

  "Mockito" should {
    "Allow mocking of methods whose argument types include a view bound, using a matcher" in {
      val receiver = mock[Receiver]
      receiver.methodWithViewBound("Testing")
      there was one(receiver).methodWithViewBound(Matchers.eq("Testing")) 
    }


    "Allow mocking of methods whose argument types include a view bound, using an argument literal" in {
      val receiver = mock[Receiver]
      receiver.methodWithViewBound("Testing")
      there was one(receiver).methodWithViewBound("Testing")
    }
  }
}

The output of this gives:

[15:18:46] [tim@ahtanum ../tim/Projects/MockitoTest] $ sbt test
[info] Set current project to Mockito View Bounds Test (in build file:/home/tim/Projects/MockitoTest/)
[info] Compiling 1 Scala source to /home/tim/Projects/MockitoTest/target/scala-2.9.1/test-classes...
[info] Mockito should
[error] x Allow mocking of methods whose argument types include a view bound
[error]     The mock was not called as expected: 
[error] Invalid use of argument matchers!
[error] 2 matchers expected, 1 recorded.
[error] This exception may occur if matchers are combined with raw values:
[error]     //incorrect:
[error]     someMethod(anyObject(), "raw String");
[error] When using matchers, all arguments have to be provided by matchers.
[error] For example:
[error]     //correct:
[error]     someMethod(anyObject(), eq("String by matcher"));
[error] 
[error] For more info see javadoc for Matchers class. (TestMockedMethodWithViewBound.scala:12)
[info]  
[info]  
[info] Total for specification TestMockedMethodWithViewBound
[info] Finished in 175 ms
[info] 1 example, 1 failure, 0 error
[error] Failed: : Total 1, Failed 1, Errors 0, Passed 0, Skipped 0
[error] Failed tests:
[error]     TestMockedMethodWithViewBound
[error] {file:/home/tim/Projects/MockitoTest/}default-3adcf2/test:test: Tests unsuccessful
[error] Total time: 7 s, completed 07-Mar-2012 15:19:47
[15:19:47] [tim@ahtanum ../tim/Projects/MockitoTest] $ sbt test
[info] Set current project to Mockito View Bounds Test (in build file:/home/tim/Projects/MockitoTest/)
[info] Compiling 1 Scala source to /home/tim/Projects/MockitoTest/target/scala-2.9.1/test-classes...
[info] Mockito should
[error] x Allow mocking of methods whose argument types include a view bound, using a matcher
[error]     The mock was not called as expected: 
[error] Invalid use of argument matchers!
[error] 2 matchers expected, 1 recorded.
[error] This exception may occur if matchers are combined with raw values:
[error]     //incorrect:
[error]     someMethod(anyObject(), "raw String");
[error] When using matchers, all arguments have to be provided by matchers.
[error] For example:
[error]     //correct:
[error]     someMethod(anyObject(), eq("String by matcher"));
[error] 
[error] For more info see javadoc for Matchers class. (TestMockedMethodWithViewBound.scala:12)
[error] x Allow mocking of methods whose argument types include a view bound, using an argument literal
[error]     The mock was not called as expected: 
[error] Argument(s) are different! Wanted:
[error] receiver.methodWithViewBound(
[error]     "Testing",
[error]     ($anonfun$apply$mcV$sp$2) <function1>
[error] );
[error] -> at TestMockedMethodWithViewBound$$anonfun$1$$anonfun$apply$6$$anonfun$apply$2.apply$mcV$sp(TestMockedMethodWithViewBound.scala:22)
[error] Actual invocation has different arguments:
[error] receiver.methodWithViewBound(
[error]     "Testing",
[error]     ($anonfun$apply$7) <function1>
[error] );
[error] -> at TestMockedMethodWithViewBound$$anonfun$1$$anonfun$apply$6.apply(TestMockedMethodWithViewBound.scala:21)
[error]  (TestMockedMethodWithViewBound.scala:19)
[info]  
[info]  
[info] Total for specification TestMockedMethodWithViewBound
[info] Finished in 325 ms
[info] 2 examples (+1), 2 expectations (+1), 2 failures (+1), 0 error
[error] Failed: : Total 2, Failed 2, Errors 0, Passed 0, Skipped 0
[error] Failed tests:
[error]     TestMockedMethodWithViewBound
[error] {file:/home/tim/Projects/MockitoTest/}default-3adcf2/test:test: Tests unsuccessful
[error] Total time: 7 s, completed 07-Mar-2012 15:23:05

…has anyone come across this problem before, or come across any way of mocking methods with view bounds or implicit parameters using specs2?

Thanks,

Tim

Answer 1

Tim, I’ve added the possibility to verify converted parameters to the latest specs2 1.9-SNAPSHOT.

This is still experimental as I don’t what kind of undesired effect could come out of that.

One thing, for example, is that any Function1 parameter will now be verified as ok by default because Mockito can not know which functions are implicit conversions and which are “regular” parameters.