option mpl-use-full-test-name breaks hash library path

[theRealSuperMario]

See #114

It looks like the paths are not correctly adapted if mpl-use-full-test-name is enabled

See tests in PR

Test output is

Can't find hash library ..

As far as I understand, the error can be narrowed down to

pytest-mpl/pytest_mpl/plugin.py

Line 462 in 7bb5d44

hash_library_filename = (Path(item.fspath).parent / hash_library_filename).absolute()

I will push a fix in #114 later.

[ConorMacBride]

From looking at #114, I think the fix was changing

        hash_library_filename = (Path(item.fspath).parent / hash_library_filename).absolute()

to

        if self.config.getini("mpl-use-full-test-name"):
            hash_library_filename = hash_library_filename.absolute()
        else:
            hash_library_filename = (Path(item.fspath).parent / hash_library_filename).absolute()

As currently documented, mpl-use-full-test-name should not affect the directory from where the hash library file is relative to. There is an issue with the hash library path, but I don't think it is related to the mpl-use-full-test-name option.

There is a separate issue (noted in #198) saying that --mpl-hash-library should be relative to where pytest was run (to match --mpl-baseline-path), which I think should solve this issue with the broken hash library path.