Question: How to expect a method only on the third invocation

[joelpresence]

Hi,

Suppose I have a test where I want some method foo to do its normal thing the first two times it is called (i.e. no mock interference) but raise an exception the third time it is called. How do I do this with rspec?

The context is something like the following:

# In some class

def bar
  foo "first invocation should succeed"
  ...
  foo "second invocation should succeed"
  ...
  foo "third invocation should raise an exception"
end

So how do I tell rspec to "leave foo alone and not override it for the first two invocations" but then "raise an exception for the third invocation using an expectation"?

I know that I can test foo separately, but I am trying to test some complex interactions here and I am unable to force method foo to raise an exception naturally (e.g. if it depends on a third party service) so I need to force it to raise an exception during the third call using an rspec expectation.

But the problem is that setting an rspec expectation overrides the method/stubs it for all three, whereas I just want the last.

Thanks! :-)

[JonRowe]

You can configure your own response logic however you want like so:

n = 0
expect(foo).to receive(:bar) do
  raise if n > 2
  n += 1
end