using mockito to mock a scala object call inside a function

Question

I'm trying to test the following function

class someClass {
    def someMethod() = {
        val x = someObject.someOtherMethod()
        //some logic that i want to test 
    }
}

Is there a way to mock val x or the someOtherMethod call without passing x

Answer 1

If SomeObject is truly an Object, I don't believe there is, short of some reflection black magic.

A common pattern is to have a trait that defines the public methods of the object, and have the object extend the trait.

Now SomeClass can depend on the SomeObject trait: e.g.

trait SomeObject {
  def someMethod: Unit
}

object SomeObject extends SomeObject {
  def someMethod = println("real method called")
}

class SomeClass(someObject: SomeObject)

and In tests you can mock the trait:

val mockObject = mock[SomeObject]
when(mockObject.someMethod).thenReturn(())
val someClass = new SomeClass(mock[SomeObject])

edit: Some Unsafe magic.

import sun.misc.Unsafe

object Foo {
  val length: String => Int = {s => s.length}
}

Foo.length("foo") // 3

val unsafe = {
  val f = classOf[Unsafe].getDeclaredField("theUnsafe")
  f.setAccessible(true)
  f.get(null).asInstanceOf[Unsafe]
}

val offset = unsafe.objectFieldOffset(Foo.getClass.getDeclaredField("length"))
val doubleLength: String => Int = { s=> s.length * 2}
unsafe.putObject(Foo, offset, doubleLength)

Foo.foo("foo") // 6

Unfortunately I couldn't make this work when Foo.length is a def and not a val