Mocking a partial (exception throwing) function - scala

Question

I'm writing a unit test using Mockito and Specs 2 in Scala. I have a class Foo with a method bar which is partially defined in the domain of its input parameter x. If the result is not defined for the given input value an FooException is thrown:
public abstract class Foo {
public abstract int bar(String x) throws FooException;
}
public class FooException extends Exception {}
Now I'm trying to create a mock using Mockito. I wish to specify that bar only returns a result for x and y and throws an exception otherwise:
import org.specs2.mutable.Specification
import org.specs2.mock.Mockito
import org.mockito.Matchers._
class FooTest extends Specification with Mockito {
val foo = mock[Foo]
foo.bar("x") returns 1
foo.bar("y") returns 2
foo.bar(anyString) throws mock[FooException]
"Foo.bar()" should {
"return an integer for x" in {
foo.bar("x") must be equalTo(1)
}
"throw an exception for z" in {
foo.bar("z") must throwA[FooException]
}
}
}
Unfortunately, this test fails. How do I write my mock in such a way that my tests pass?
Update
The tests fail because an exception is thrown at runtime. The code above results in:
java.lang.NullPointerException
[error] Could not run test FooTest: java.lang.NullPointerException
If I change the order, as suggested in one of the answers, I get the following stack trace:
[error] Could not create an instance of FooTest
[error] caused by java.lang.Exception: Could not instantiate class FooTest: null
[error] org.specs2.reflect.Classes$class.tryToCreateObjectEither(Classes.scala:93)
[error] org.specs2.reflect.Classes$.tryToCreateObjectEither(Classes.scala:207)
[error] org.specs2.specification.SpecificationStructure$$anonfun$createSpecificationEither$2.apply(BaseSpecification.scala:119)
[error] org.specs2.specification.SpecificationStructure$$anonfun$createSpecificationEither$2.apply(BaseSpecification.scala:119)
[error] scala.Option.getOrElse(Option.scala:120)
[error] org.specs2.specification.SpecificationStructure$.createSpecificationEither(BaseSpecification.scala:119)
[error] org.specs2.runner.SbtRunner.org$specs2$runner$SbtRunner$$specificationRun(SbtRunner.scala:73)
[error] org.specs2.runner.SbtRunner$$anonfun$newTask$1$$anon$5.execute(SbtRunner.scala:59)
[error] sbt.TestRunner.runTest$1(TestFramework.scala:84)
[error] sbt.TestRunner.run(TestFramework.scala:94)
[error] sbt.TestFramework$$anon$2$$anonfun$$init$$1$$anonfun$apply$8.apply(TestFramework.scala:219)
[error] sbt.TestFramework$$anon$2$$anonfun$$init$$1$$anonfun$apply$8.apply(TestFramework.scala:219)
[error] sbt.TestFramework$.sbt$TestFramework$$withContextLoader(TestFramework.scala:207)
[error] sbt.TestFramework$$anon$2$$anonfun$$init$$1.apply(TestFramework.scala:219)
[error] sbt.TestFramework$$anon$2$$anonfun$$init$$1.apply(TestFramework.scala:219)
[error] sbt.TestFunction.apply(TestFramework.scala:224)
[error] sbt.Tests$$anonfun$7.apply(Tests.scala:196)
[error] sbt.Tests$$anonfun$7.apply(Tests.scala:196)
[error] sbt.std.Transform$$anon$3$$anonfun$apply$2.apply(System.scala:45)
[error] sbt.std.Transform$$anon$3$$anonfun$apply$2.apply(System.scala:45)
[error] sbt.std.Transform$$anon$4.work(System.scala:64)
[error] sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:237)
[error] sbt.Execute$$anonfun$submit$1$$anonfun$apply$1.apply(Execute.scala:237)
[error] sbt.ErrorHandling$.wideConvert(ErrorHandling.scala:18)
[error] sbt.Execute.work(Execute.scala:244)
[error] sbt.Execute$$anonfun$submit$1.apply(Execute.scala:237)
[error] sbt.Execute$$anonfun$submit$1.apply(Execute.scala:237)
[error] sbt.ConcurrentRestrictions$$anon$4$$anonfun$1.apply(ConcurrentRestrictions.scala:160)
[error] sbt.CompletionService$$anon$2.call(CompletionService.scala:30)
[error] java.util.concurrent.FutureTask.run(FutureTask.java:262)
[error] java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
[error] java.util.concurrent.FutureTask.run(FutureTask.java:262)
[error] java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
[error] java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
[error] java.lang.Thread.run(Thread.java:744)
[error] caused by java.lang.NullPointerException

Answer 1

You need to change the order of your stubbing around. Stub the generalized behavior first (anyString) and then add more specific behaviors after that. So do this:
val foo = mock[Foo]
foo.bar(anyString) throws mock[FooException]
foo.bar("x") returns 1
foo.bar("y") returns 2

Answer 2

You could set up a callback on the mock:
val foo = mock[Foo]
foo.bar(anyString) answers (derp => {
derp match {
case "x" => 1
case "y" => 2
case _ => throw mock[FooException]
}
})
There are some more details in the specs2 documentation.