Add a test for yielding with an operator

[duncan3dc]

As pointed out on internals there is a valid yield syntax that is not currently tested for.

I've attempted to add a test for this, let me know if there's anything that needs changing or doesn't make sense.

[pierredup]

What about testing the +, - and / operators as well?
There seems to already be a regression when using operators on yield since PHP 7

https://bugs.php.net/bug.php?id=69160
http://3v4l.org/JQdt6
http://3v4l.org/U5iki

[duncan3dc]

I've updated the test with the other operators now, and + & - are failing, as reported by @pierredup

[php-pulls]

Comment on behalf of bwoebi at php.net:

How can I now yield a literal negative number?

yield -1; does what? It yields -1 (in 5.5/5.6 too). [As long as it's a standalone statement, or it will require parenthesis in PHP 5.x.]

Now it'd be very surprising if that changed and yielded null (the implicit default value) in PHP 7.
Or do you want to really make behavior dependent on if the return value is used? That'd be really weird...

Closing as bogus test (Bug report left open for @nikic to add a note to UPGRADING).

I will add some test for the new behavior though, to explicitly document that.