Don't display dict common items if verbosity=1

Part one of pytest-dev#1512.

If verbosity=1, assertion explanations are truncated at 10 lines. In this
situation, it's more important to tell the user which dictionary items are
different than which are the same.

_pytest/assertion/util.py

@@ -256,8 +256,8 @@ def _compare_eq_dict(left, right, verbose=False):
     explanation = []
     common = set(left).intersection(set(right))
     same = dict((k, left[k]) for k in common if left[k] == right[k])
-    if same and not verbose:
-        explanation += [u('Omitting %s identical items, use -v to show') %
+    if same and verbose < 2:
+        explanation += [u('Omitting %s identical items, use -vv to show') %
                         len(same)]
     elif same:
         explanation += [u('Common items:')]

testing/test_assertion.py

@@ -361,8 +361,16 @@ def test_dict_omitting(self):
         for line in lines[1:]:
             assert 'b' not in line
 
-    def test_dict_omitting_verbose(self):
-        lines = callequal({'a': 0, 'b': 1}, {'a': 1, 'b': 1}, verbose=True)
+    def test_dict_omitting_with_verbosity_1(self):
+        """ Ensure differing items are visible for verbosity=1 (#1512) """
+        lines = callequal({'a': 0, 'b': 1}, {'a': 1, 'b': 1}, verbose=1)
+        assert lines[1].startswith('Omitting 1 identical item')
+        assert lines[2].startswith('Differing items')
+        assert lines[3] == "{'a': 0} != {'a': 1}"
+        assert 'Common items' not in lines
+
+    def test_dict_omitting_with_verbosity_2(self):
+        lines = callequal({'a': 0, 'b': 1}, {'a': 1, 'b': 1}, verbose=2)
         assert lines[1].startswith('Common items:')
         assert 'Omitting' not in lines[1]
         assert lines[2] == "{'b': 1}"