Create some way to do stub a function a certain number of times

[sarahsturgeon]

When making a stub, it may be desirable to only stub the function for a single call.

You can do this now, like:

local hookStub

hookStub = stub( hook, "Call" ).with( function()
    hookStub:Restore()
end )

hook.Call( "blah" )

expect( hookStub ).to.haveBeenCalled()

But if you don't localize hookStub first, as would be common for these sorts of tests:

local hookStub = stub( hook, "Call" ).with( function()
    hookStub:Restore()
end )

You would get an error on your hook.Call invocation, with the error message attempt to index global 'hookStub', a nil value.

This of course makes sense, but it can be confusing. Instead, perhaps we could have something like:

local hookStub = stubOnce( hook, "Call" )

hook.Call( "blah" )

expect( hookStub ).to.haveBeenCalled()

More realistically, we should allow a hook to be stubbed for any number of calls. Maybe as an optional third parameter to stub()?