How to mock tail recursive functions?

Question

I want to test my code which has a few tail recursive functions. I couldn't mock the tail recursive functions because they need to declared either Final or Private. Most mocking frameworks don't support mocking such methods, the ones that support isn't working as expected.

Is this possible at all? Can some one provide me their ideas to mock tail recursive functions?

I tried mocking using Mockito Framework version 3.0.0. My Test suite is extended with the Mockito-Sugar trait.

Though mockito documentation suggests that final methods can be mocked, It results in failure for me.

I tried using scala-mock. I faced different problems and didn't work out.

Tim Tim · Accepted Answer · 2019-07-28T13:27:13

One way to fix this is to wrap the recursive code in an outer function. For example:

def factorial(n: Int): Int = {
  @annotation.tailrec
  def loop(i: Int, res: Int): Int =
    if (i <= 1) {
      res
    } else {
      loop(i-1, i*res)
    }

  loop(n-1, n)
}

Using this pattern the factorial method does not need to be final or private so it can be overridden for testing.

Another advantage of this pattern is that the accumulator value res does not have to be exposed in the main function interface. This pattern also allows special cases to be handled outside the main recursive code, making the inner code simpler and potentially faster.

How to mock tail recursive functions?

1 Answers