Parameterize wheel file path for metadata extraction

src/pip/_internal/utils/wheel.py

@@ -93,18 +93,21 @@ def wheel_metadata(source, dist_info_dir):
     """Return the WHEEL metadata of an extracted wheel, if possible.
     Otherwise, raise UnsupportedWheel.
     """
+    # Zip file path separators must be /
+    path = "{}/WHEEL".format(dist_info_dir)
     try:
-        # Zip file path separators must be /
-        wheel_contents = source.read("{}/WHEEL".format(dist_info_dir))
+        wheel_contents = source.read(path)
         # BadZipFile for general corruption, KeyError for missing entry,
         # and RuntimeError for password-protected files
     except (BadZipFile, KeyError, RuntimeError) as e:
-        raise UnsupportedWheel("could not read WHEEL file: {!r}".format(e))
+        raise UnsupportedWheel(
+            "could not read {!r} file: {!r}".format(path, e)
+        )
 
     try:
         wheel_text = ensure_str(wheel_contents)
     except UnicodeDecodeError as e:
-        raise UnsupportedWheel("error decoding WHEEL: {!r}".format(e))
+        raise UnsupportedWheel("error decoding {!r}: {!r}".format(path, e))
 
     # FeedParser (used by Parser) does not raise any exceptions. The returned
     # message may have .defects populated, but for backwards-compatibility we

tests/unit/test_utils_wheel.py

@@ -85,7 +85,7 @@ def test_wheel_metadata_fails_missing_wheel(tmpdir, zip_dir):
 
     with pytest.raises(UnsupportedWheel) as e:
         wheel.wheel_metadata(zip_dir(tmpdir), dist_info_dir.name)
-    assert "could not read WHEEL file" in str(e.value)
+    assert "could not read" in str(e.value)
 
 
 @skip_if_python2
@@ -97,7 +97,7 @@ def test_wheel_metadata_fails_on_bad_encoding(tmpdir, zip_dir):
 
     with pytest.raises(UnsupportedWheel) as e:
         wheel.wheel_metadata(zip_dir(tmpdir), dist_info_dir.name)
-    assert "error decoding WHEEL" in str(e.value)
+    assert "error decoding" in str(e.value)
 
 
 def test_wheel_version_fails_on_no_wheel_version():