mock a function with a callback function as parameter

My code structure is l开发者_StackOverflowike below:

class A {
  def a(x: () => Unit) { do something}
}

class B {
  .... 
  def foo() {
    def x() { something }
    a(x)
  }
}

Now I want to do unittest of class B with a mock A.

val a = mock[A]
def x () { ... }
a.a(x) atLeastOnce

The above doesn't work. Since this new x is not the x inside foo(). But the x inside foo is a local one, not accessible to unittest. Any suggestion except to move x out of foo?

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You have to mock out the function literal passed into A.a. Please look into the answer of the following SOF question and see whether that helps

How to mock a method with functional arguments in Scala?