Check if function humbug_phpscoper_expose_class exists

[leoloso]

Fixes #809

@theofidry I can't run the tests locally, as composer update is failing (am I doing something wrong?):

  Problem 1
    - humbug/box[4.0.0, ..., 4.2.0] require composer-plugin-api ^2.2 -> found composer-plugin-api[2.1.0] but it does not match the constraint.
    - Root composer.json requires humbug/box ^4.0 -> satisfiable by humbug/box[4.0.0, ..., 4.2.0].

But I can see the tests are passing here on GitHub

[theofidry]

I can't run the tests locally, as composer update is failing (am I doing something wrong?)

If you do make phpunit it should work. The issue is that you need to source .composer-root-version since there is a circular dependency (in dev) with Box.

[theofidry]

👍 The patch looks good to me thanks!

I would like to capture this into a dedicated test for the future so I'll hold off a bit for the merge. Hopefully I should be able to figure it out soon :)

[theofidry]

Thanks a lot @leoloso!

[leoloso]

Thanks to you @theofidry 😃