Add test case to check getCoverArt's functionality

Mock two functions `getCoverArt`, `get_image_front` and use
a locally available cover art to check if the created cover
art exists.

Problems:
- How to check image's quality.
- Not sure if only this check is enough (do we need to check the
embedding part?).

Signed-off-by: ABCbum <kimlong221002@gmail.com>

whipper/command/cd.py

@@ -497,6 +497,10 @@ Log files will log the path to tracks relative to this directory.
                 continue
             _ripIfNotRipped(i + 1)
 
+        # NOTE: Seems like some kind of with … or try: … finally: … clause
+        # would be more appropriate, since otherwise this would potentially
+        # leave stray files lying around in case of crashes etc.
+        # <Freso 2020-01-03, GitHub comment>
         if (self.options.fetch_cover_art == "embed" and
                 self.coverArtPath is not None):
             logger.debug('deleting cover art file at: %r', self.coverArtPath)

whipper/test/test_common_program.py

@@ -2,8 +2,10 @@
 # vi:si:et:sw=4:sts=4:ts=4
 
 
+import os
 import unittest
 
+from tempfile import NamedTemporaryFile
 from whipper.common import program, mbngs, config
 from whipper.command.cd import DEFAULT_DISC_TEMPLATE
 
@@ -38,3 +40,54 @@ class PathTestCase(unittest.TestCase):
         path = prog.getPath('/tmp', '%A/%d', 'mbdiscid', md, 0)
         self.assertEqual(path,
                          '/tmp/Jeff Buckley/Grace')
+
+
+# TODO: Test cover art embedding too.
+class CoverArtTestCase(unittest.TestCase):
+
+    @staticmethod
+    def _mock_get_front_image(release_id):
+        """
+        Mock `musicbrainzngs.get_front_image` function.
+
+        Reads a local cover art image and returns its binary data.
+
+        :param release_id: a release id (self.program.metadata.mbid)
+        :type  release_id: str
+        :returns: the binary content of the local cover art image
+        :rtype: bytes
+        """
+        filename = '%s.jpg' % release_id
+        path = os.path.join(os.path.dirname(__file__), filename)
+        with open(path, 'rb') as f:
+            return f.read()
+
+    def _mock_getCoverArt(self, path, release_id):
+        """
+        Mock `common.program.getCoverArt` function.
+
+        :param path: where to store the fetched image
+        :type  path: str
+        :param release_id: a release id (self.program.metadata.mbid)
+        :type  release_id: str
+        :returns: path to the downloaded cover art
+        :rtype: str
+        """
+        cover_art_path = os.path.join(path, 'cover.jpg')
+
+        data = self._mock_get_front_image(release_id)
+
+        with NamedTemporaryFile(suffix='.cover.jpg', delete=False) as f:
+            f.write(data)
+        os.chmod(f.name, 0o644)
+        os.replace(f.name, cover_art_path)
+        return cover_art_path
+
+    def testCoverArtPath(self):
+        """Test whether a fetched cover art is saved properly."""
+        # Using: Dummy by Portishead
+        # https://musicbrainz.org/release/76df3287-6cda-33eb-8e9a-044b5e15ffdd
+        path = os.path.dirname(__file__)
+        release_id = "76df3287-6cda-33eb-8e9a-044b5e15ffdd"
+        coverArtPath = self._mock_getCoverArt(path, release_id)
+        self.assertTrue(os.path.isfile(coverArtPath))