Make stub_with work with skip_optional_callbacks

[flurin]

Checks if the mock actually exports the function before it defines the stub. Fixes #95

[josevalim]

We should only skip if they are optional though. Otherwise we can stop raising for functions that are required .

[flurin]

I'm not sure because this checks if the mock function had been defined on the mock. So when you use skip_optional_callbacks with a specific set of callbacks it still works correctly.

Just checking if it's optional wouldn't cover that, right?

[josevalim]

I see, I misunderstood. Looks good as is then!

[josevalim]

Something along these lines:

for behaviour <- behaviours,
    optional = behaviour.behaviour_info(:optional_callbacks),
    {fun, arity} <- behaviour.behaviour_info(:callbacks) do
  if function_exported?(mock, fun, arity) or {fun, arity} not in optional do

We should add a test that stub_with fails when some non-optional callback is missing.

[flurin]

I agree that you should always implement the full behaviour in the Stub module, but enforcing this would possibly break a lot of current usage. Currently this test succeeds:

    defmodule PartialCalcImplementation do
      @behaviour Calculator
      def add(x, y), do: x + y
    end

    test "partial" do
      in_all_modes(fn ->
        stub_with(CalcMock, PartialCalcImplementation)
        assert CalcMock.add(1, 2) == 3

        assert_raise UndefinedFunctionError, fn ->
          assert CalcMock.mult(3, 4)
        end
      end)
    end

[flurin]

I'd be happy to change that you can only stub full behaviour implementations of course.

[josevalim]

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