add spec for Fiber#raise

[kuei0221]

This PR is for solving #745, add spec of Fiber#raise. I am not very familiar with Fiber, so tell me if anything needs to improve 😄

Added Fiber#raise that behaves like Fiber#resume but raises an
exception on the resumed fiber. Feature #10344

[eregon]

Fiber#raise is actually a core method (it does not need require 'fiber' unlike e.g. Fiber#transfer), so it should be in core/fiber/raise_spec.rb

[eregon]

This a good start but needs some fixes.

[eregon]

This will define a new global constant, it should instead be nested under module FiberSpecs, or Class.new(StandardError) be used instead.

[eregon]

The spec descriptions should form a sentence, so typically the first word will be a 3rd person present verb like raises/accepts/does not accept, etc.

[eregon]

There are specs for Kernel/Thread#raise (https://github.com/ruby/spec/blob/master/shared/kernel/raise.rb) we should be able to reuse here, like so:

module FiberSpecs
  class NewFiberToRaise
    def self.raise(*args)
      fiber = Fiber.new { Fiber.yield }
      fiber.resume
      fiber.raise(*args)
    end
  end
end

  describe "Fiber#raise" do
    it_behaves_like :kernel_raise, :raise, FiberSpecs::NewFiberToRaise
  end

[kuei0221]

Thanks for your comment! I have followed your suggestion and update the code, everything works fine except one.
One of the shared test will fail:

Fiber#raise re-raises a previously rescued exception without overwriting the backtrace FAILED
Expected "/Users/michaelhuang/spec/core/fiber/fixtures/classes.rb:4:in `yield'"
to include "/Users/michaelhuang/spec/shared/kernel/raise.rb:55:"
/Users/michaelhuang/spec/shared/kernel/raise.rb:66:in `rescue in rescue in block (2 levels) in <top (required)>'
/Users/michaelhuang/spec/shared/kernel/raise.rb:57:in `rescue in block (2 levels) in <top (required)>'
/Users/michaelhuang/spec/shared/kernel/raise.rb:54:in `block (2 levels) in <top (required)>'
/Users/michaelhuang/spec/core/fiber/raise.rb:6:in `block in <top (required)>'
/Users/michaelhuang/spec/core/fiber/raise.rb:5:in `<top (required)>'

I think Fiber has a different mechanism here.
In the case of Kernel or Thread (other class also shared :kernel_raise), an exception will happen at the file where raise was called.

Fiber does not, it will jump to the file where Fiber yield was and throw an exception. Not active by raise.
If my understanding is correct, I will have to skip this test when class is Fiber, or maybe isolate it to another shared example. And then add another test to cover this feature.

[eregon]

@kuei0221 I think that's simply of the extra indirection we have for Fiber#raise with the FiberSpecs::NewFiberToRaise.raise helper.
Could you push what you have so far?
Then I'll find a way to address that spec.

[eregon]

Thank you for the new specs!