test loading samples from a corrupted audio file

Verify that the correct exception is raised by the C extension. I'm not
sure why I didn't cover this code path before. It only makes sense to
test this path in checksums(), because nframes() does not try to load
the samples (it only reads the header).

corrupted.flac is a copy of sample.flac where some of the values were
overwritten with garbage in a hex editor, so that testing the file with
"flac -t" results in an error.

tests/_audio_test.py

@@ -14,6 +14,7 @@
 CWD = os.path.abspath(os.path.dirname(__file__))
 NOT_AUDIO_PATH = CWD + '/data/samples/not_audio'
 SAMPLE_VORBIS_PATH = CWD + '/data/samples/sample.ogg'
+CORRUPTED_AUDIO_PATH = CWD + '/data/samples/corrupted.flac'
 
 
 class TestExceptionsChecksums(unittest.TestCase):
@@ -41,6 +42,10 @@ def test_unsupported_audio_format(self):
         with self.assertRaisesRegex(TypeError, 'Unsupported audio format'):
             _audio.checksums(SAMPLE_VORBIS_PATH, 1, 9)
 
+    def test_corrupted_audio(self):
+        with self.assertRaisesRegex(OSError, 'Failed to load audio samples'):
+            _audio.checksums(CORRUPTED_AUDIO_PATH, 1, 9)
+
 
 class TestExceptionsNframes(unittest.TestCase):
     """Test exceptions raised when getting the number of audio frames in a file."""