Consolidate tests for packaging.metadata.

New tests were added in test_metadata and old tests inherited from
distutils were still in test_dist, so I moved them into test_metadata
(except for one which was more at home in test_run) and merged
duplicates.

I also added some skips to lure contributors <wink>, optimized the
Metadata.update method a trifle, and added notes about a number of
issues.

A note: The tests in test_dist used to dump the Metadata objects to a
file in the METADATA format and look for strings in its contents; I
updated them to use the mapping API of Metadata instead.  For some
fields with special writing rules, I have added tests to ensure my
conversion did not lose anything.

1 files changed, 12 insertions, 2 deletions

diff --git a/Lib/packaging/metadata.py b/Lib/packaging/metadata.py
index 104600b..7d7fc6b 100644
--- a/Lib/packaging/metadata.py
+++ b/Lib/packaging/metadata.py
@@ -354,11 +354,20 @@ class Metadata:
         Keys that don't match a metadata field or that have an empty value are
         dropped.
         """
+        # XXX the code should just use self.set, which does tbe same checks and
+        # conversions already, but that would break packaging.pypi: it uses the
+        # update method, which does not call _set_best_version (which set
+        # does), and thus allows having a Metadata object (as long as you don't
+        # modify or write it) with extra fields from PyPI that are not fields
+        # defined in Metadata PEPs.  to solve it, the best_version system
+        # should be reworked so that it's called only for writing, or in a new
+        # strict mode, or with a new, more lax Metadata subclass in p7g.pypi
         def _set(key, value):
             if key in _ATTR2FIELD and value:
                 self.set(self._convert_name(key), value)
 
-        if other is None:
+        if not other:
+            # other is None or empty container
             pass
         elif hasattr(other, 'keys'):
             for k in other.keys():
@@ -368,7 +377,8 @@ class Metadata:
                 _set(k, v)
 
         if kwargs:
-            self.update(kwargs)
+            for k, v in kwargs.items():
+                _set(k, v)
 
     def set(self, name, value):
         """Control then set a metadata field."""