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.

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."""

Lib/packaging/tests/test_run.py

@@ -3,16 +3,16 @@
 import os
 import sys
 import shutil
-from tempfile import mkstemp
 from io import StringIO
 
 from packaging import install
 from packaging.tests import unittest, support, TESTFN
 from packaging.run import main
 
+from test.script_helper import assert_python_ok
+
 # setup script that uses __file__
 setup_using___file__ = """\
-
 __file__
 
 from packaging.run import setup
@@ -20,7 +20,6 @@ setup()
 """
 
 setup_prints_cwd = """\
-
 import os
 print os.getcwd()
 
@@ -29,11 +28,12 @@ setup()
 """
 
 
-class CoreTestCase(support.TempdirManager, support.LoggingCatcher,
-                   unittest.TestCase):
+class RunTestCase(support.TempdirManager,
+                  support.LoggingCatcher,
+                  unittest.TestCase):
 
     def setUp(self):
-        super(CoreTestCase, self).setUp()
+        super(RunTestCase, self).setUp()
         self.old_stdout = sys.stdout
         self.cleanup_testfn()
         self.old_argv = sys.argv, sys.argv[:]
@@ -43,7 +43,7 @@ class CoreTestCase(support.TempdirManager, support.LoggingCatcher,
         self.cleanup_testfn()
         sys.argv = self.old_argv[0]
         sys.argv[:] = self.old_argv[1]
-        super(CoreTestCase, self).tearDown()
+        super(RunTestCase, self).tearDown()
 
     def cleanup_testfn(self):
         path = TESTFN
@@ -77,9 +77,16 @@ class CoreTestCase(support.TempdirManager, support.LoggingCatcher,
             os.chmod(install_path, old_mod)
             install.get_path = old_get_path
 
+    def test_show_help(self):
+        # smoke test, just makes sure some help is displayed
+        status, out, err = assert_python_ok('-m', 'packaging.run', '--help')
+        self.assertEqual(status, 0)
+        self.assertGreater(out, b'')
+        self.assertEqual(err, b'')
+
 
 def test_suite():
-    return unittest.makeSuite(CoreTestCase)
+    return unittest.makeSuite(RunTestCase)
 
 if __name__ == "__main__":
     unittest.main(defaultTest="test_suite")