Added test for readonly properties from parent scope variable

[Wedrix]

This PR adds a failing test for #58.

In the test, the closure inherits an object which uses readonly properties from the parent scope.
This causes an error when the closure gets deserialised as explained by @theofidry.

[nunomaduro]

Thank you for this. Are you able to now, adjust the source code to solve the issue? You probably want to add a few more tests.

[GrahamCampbell]

This probably a no-fix. It is not possible to by-pass readonly, even using reflection.

[driesvints]

@Wedrix what are your thoughts on @GrahamCampbell's comment?

[Wedrix]

@Wedrix what are your thoughts on @GrahamCampbell's comment?

Found this somewhere in the PHP docs. It may be possible depending on the implementation. I am yet to study the code.

[nunomaduro]

I am afraid this issue is unfixable, because it's literally impossible to set readonly properties using reflection. Feel free to make a pull request if you can come up with a solution.

[Wedrix]

@nunomaduro if it cannot be fixed then maybe it should be documented as one the caveats?

[theofidry]

Thanks for investigating this @Wedrix! I remember going a bit nuts on that issue not finding the cause, good to know why now.