tests relying on /dev/cdrom failing when running with pytest

[dvzrv]

Hi! When packaging 1.2.0 for Arch Linux I used pytest to run the test suite (i.e. pytest -v). The way of running tests via setuptools (i.e. python setup.py test) is soon going to be deprecated hence I'm rather switching earlier than later ;-)
Unfortunately a few of the tests seem to have defaults set that can not be met (also because they assume that a cdrom drive is available. We run packaging tools in pristine systemd-nspawn containers which is why there will never be a cdrom drive though.

============================= test session starts ==============================
platform linux -- Python 3.8.5, pytest-6.0.1, py-1.9.0, pluggy-0.13.1 -- /usr/bin/python
cachedir: .pytest_cache
rootdir: /build/python-discid/src/python-discid-1.2.0
collecting ... collected 16 items

test_discid.py::TestModulePrivate::test_decode PASSED                    [  6%]
test_discid.py::TestModulePrivate::test_encode PASSED                    [ 12%]
test_discid.py::TestModulePrivate::test_encoding PASSED                  [ 18%]
test_discid.py::TestModule::test_default_device PASSED                   [ 25%]
test_discid.py::TestModule::test_device_encoding PASSED                  [ 31%]
test_discid.py::TestModule::test_features PASSED                         [ 37%]
test_discid.py::TestModule::test_features_implemented PASSED             [ 43%]
test_discid.py::TestModule::test_invalid_device PASSED                   [ 50%]
test_discid.py::TestModule::test_put_fail PASSED                         [ 56%]
test_discid.py::TestModule::test_put_success PASSED                      [ 62%]
test_discid.py::TestModule::test_version_string PASSED                   [ 68%]
test_discid.py::TestDisc::test_default_device PASSED                     [ 75%]
test_discid.py::TestDisc::test_features PASSED                           [ 81%]
test_discid.py::TestDisc::test_read_features FAILED                      [ 87%]
test_discid.py::TestDisc::test_read_put FAILED                           [ 93%]
test_discid.py::TestDisc::test_read_simple FAILED                        [100%]

=================================== FAILURES ===================================
_________________________ TestDisc.test_read_features __________________________

self = <test_discid.TestDisc testMethod=test_read_features>

    def test_read_features(self):
>       disc = discid.read(features=["mcn", "isrc"]) # read from default drive

test_discid.py:178:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
discid/disc.py:55: in read
    disc.read(device, features)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <discid.disc.Disc object at 0x6bc3e9d7f970>, device = None
features = ['mcn', 'isrc']

    def read(self, device=None, features=[]):
        """Reads the TOC from the device given as string

        The user is supposed to use :func:`discid.read`.
        """
        if "read" not in FEATURES:
            raise NotImplementedError("discid_read not implemented on platform")

        # only use features implemented on this platform and in this module
        self._requested_features = list(set(features) & set(FEATURES)
                                        & set(FEATURES_IMPLEMENTED))

        # create the bitmask for libdiscid
        c_features = 0
        for feature in features:
            c_features += _FEATURE_MAPPING.get(feature, 0)

        # device = None will use the default device (internally)
        try:
            result = _LIB.discid_read_sparse(self._handle, _encode(device),
                                             c_features) == 1
        except AttributeError:
            result = _LIB.discid_read(self._handle, _encode(device)) == 1
        self._success = result
        if not self._success:
>           raise DiscError(self._get_error_msg())
E           discid.disc.DiscError: cannot open device `/dev/cdrom'

discid/disc.py:152: DiscError
____________________________ TestDisc.test_read_put ____________________________

self = <test_discid.TestDisc testMethod=test_read_put>

    def test_read_put(self):
        # a read followed with a put, which should clear the features
>       disc = discid.read(features=["mcn", "isrc"]) # read from default drive

test_discid.py:196:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
discid/disc.py:55: in read
    disc.read(device, features)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <discid.disc.Disc object at 0x6bc3e9d0c700>, device = None
features = ['mcn', 'isrc']

    def read(self, device=None, features=[]):
        """Reads the TOC from the device given as string

        The user is supposed to use :func:`discid.read`.
        """
        if "read" not in FEATURES:
            raise NotImplementedError("discid_read not implemented on platform")

        # only use features implemented on this platform and in this module
        self._requested_features = list(set(features) & set(FEATURES)
                                        & set(FEATURES_IMPLEMENTED))

        # create the bitmask for libdiscid
        c_features = 0
        for feature in features:
            c_features += _FEATURE_MAPPING.get(feature, 0)

        # device = None will use the default device (internally)
        try:
            result = _LIB.discid_read_sparse(self._handle, _encode(device),
                                             c_features) == 1
        except AttributeError:
            result = _LIB.discid_read(self._handle, _encode(device)) == 1
        self._success = result
        if not self._success:
>           raise DiscError(self._get_error_msg())
E           discid.disc.DiscError: cannot open device `/dev/cdrom'

discid/disc.py:152: DiscError
__________________________ TestDisc.test_read_simple ___________________________
self = <test_discid.TestDisc testMethod=test_read_simple>

    def test_read_simple(self):
>       disc = discid.read()        # read from default drive

test_discid.py:123:
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
discid/disc.py:55: in read
    disc.read(device, features)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

self = <discid.disc.Disc object at 0x6bc3e9cd2640>, device = None, features = []

    def read(self, device=None, features=[]):
        """Reads the TOC from the device given as string

        The user is supposed to use :func:`discid.read`.
        """
        if "read" not in FEATURES:
            raise NotImplementedError("discid_read not implemented on platform")

        # only use features implemented on this platform and in this module
        self._requested_features = list(set(features) & set(FEATURES)
                                        & set(FEATURES_IMPLEMENTED))

        # create the bitmask for libdiscid
        c_features = 0
        for feature in features:
            c_features += _FEATURE_MAPPING.get(feature, 0)

        # device = None will use the default device (internally)
        try:
            result = _LIB.discid_read_sparse(self._handle, _encode(device),
                                             c_features) == 1
        except AttributeError:
            result = _LIB.discid_read(self._handle, _encode(device)) == 1
        self._success = result
        if not self._success:
>           raise DiscError(self._get_error_msg())
E           discid.disc.DiscError: cannot open device `/dev/cdrom'

discid/disc.py:152: DiscError
=========================== short test summary info ============================
FAILED test_discid.py::TestDisc::test_read_features - discid.disc.DiscError: ...
FAILED test_discid.py::TestDisc::test_read_put - discid.disc.DiscError: canno...
FAILED test_discid.py::TestDisc::test_read_simple - discid.disc.DiscError: ca...
========================= 3 failed, 13 passed in 0.13s =========================

I will disable these tests for now, as they can never be met in a packaging environment. Maybe they can be changed so that they are skipped if no cdrom drive is available?