adding docs and cleaning up

changelog/3632.feature.rst

@@ -1 +1 @@
-Richer comparison information on ``AssertionError`` for objects created using `attrs <http://www.attrs.org/en/stable/>`_ or `dataclasses <https://docs.python.org/3/library/dataclasses.html>`_ (Python 3.7+).
+Richer comparison introspection on ``AssertionError`` for objects created using `attrs <http://www.attrs.org/en/stable/>`_ or `dataclasses <https://docs.python.org/3/library/dataclasses.html>`_ (Python 3.7+).

doc/en/example/assertion/failure_demo.py

@@ -101,6 +101,30 @@ class TestSpecialisedExplanations(object):
         text = "head " * 50 + "f" * 70 + "tail " * 20
         assert "f" * 70 not in text
 
+    def test_eq_dataclass(self):
+        from dataclasses import dataclass
+
+        @dataclass
+        class Foo(object):
+            a: int
+            b: str
+
+        left = Foo(1, "b")
+        right = Foo(1, "c")
+        assert left == right
+
+    def test_eq_attrs(self):
+        import attr
+
+        @attr.s
+        class Foo(object):
+            a = attr.ib()
+            b = attr.ib()
+
+        left = Foo(1, "b")
+        right = Foo(1, "c")
+        assert left == right
+
 
 def test_attribute():
     class Foo(object):

doc/en/example/assertion/test_failures.py

@@ -9,5 +9,5 @@ def test_failure_demo_fails_properly(testdir):
     failure_demo.copy(target)
     failure_demo.copy(testdir.tmpdir.join(failure_demo.basename))
     result = testdir.runpytest(target, syspathinsert=True)
-    result.stdout.fnmatch_lines(["*42 failed*"])
+    result.stdout.fnmatch_lines(["*44 failed*"])
     assert result.ret != 0

src/_pytest/assertion/util.py

@@ -347,12 +347,12 @@ def _compare_eq_class(left, right, verbose, type=None):
     if same and verbose < 2:
         explanation += [u("Omitting %s identical items, use -vv to show") % len(same)]
     elif same:
-        explanation += [u("Common items:")]
+        explanation += [u("Common attributes:")]
         explanation += pprint.pformat(same).splitlines()
     if diff:
+        class_name = left.__class__.__name__
         explanation += [("Differing attributes:")]
         for k in diff:
-            class_name = left.__class__.__name__
             explanation += [
                 u("%s(%s=%r) != %s(%s=%r)")
                 % (class_name, k, getattr(left, k), class_name, k, getattr(right, k))

testing/test_assertion.py

@@ -564,7 +564,7 @@ class TestAssert_reprcompare_dataclass(object):
 
         lines = callequal(left, right)
         assert lines[1].startswith("Omitting 1 identical item")
-        assert "Common items" not in lines
+        assert "Common attributes" not in lines
         for line in lines[1:]:
             assert "field_a" not in line
 
@@ -581,7 +581,7 @@ class TestAssert_reprcompare_dataclass(object):
         right = SimpleDataObject(1, "c")
 
         lines = callequal(left, right, verbose=2)
-        assert lines[1].startswith("Common items:")
+        assert lines[1].startswith("Common attributes:")
         assert "Omitting" not in lines[1]
         assert lines[2] == "['field_a']"
 
@@ -598,14 +598,14 @@ class TestAssert_reprcompare_dataclass(object):
         right = SimpleDataObject(1, "b")
 
         lines = callequal(left, right, verbose=2)
-        assert lines[1].startswith("Common items:")
+        assert lines[1].startswith("Common attributes:")
         assert "Omitting" not in lines[1]
         assert lines[2] == "['field_a']"
         for line in lines[2:]:
             assert "field_b" not in line
 
     @pytest.mark.skipif(sys.version_info < (3, 7), reason="Dataclasses in Python3.7+")
-    def test_comparing_different_data_classes(self):
+    def test_comparing_two_different_data_classes(self):
         from dataclasses import dataclass
 
         @dataclass
@@ -637,7 +637,7 @@ class TestAssert_reprcompare_attrsclass(object):
 
         lines = callequal(left, right)
         assert lines[1].startswith("Omitting 1 identical item")
-        assert "Common items" not in lines
+        assert "Common attributes" not in lines
         for line in lines[1:]:
             assert "field_a" not in line
 
@@ -651,7 +651,7 @@ class TestAssert_reprcompare_attrsclass(object):
         right = SimpleDataObject(1, "c")
 
         lines = callequal(left, right, verbose=2)
-        assert lines[1].startswith("Common items:")
+        assert lines[1].startswith("Common attributes:")
         assert "Omitting" not in lines[1]
         assert lines[2] == "['field_a']"
 
@@ -665,13 +665,13 @@ class TestAssert_reprcompare_attrsclass(object):
         right = SimpleDataObject(1, "b")
 
         lines = callequal(left, right, verbose=2)
-        assert lines[1].startswith("Common items:")
+        assert lines[1].startswith("Common attributes:")
         assert "Omitting" not in lines[1]
         assert lines[2] == "['field_a']"
         for line in lines[2:]:
             assert "field_b" not in line
 
-    def test_comparing_different_attrs(self):
+    def test_comparing_two_different_attrs_classes(self):
         @attr.s
         class SimpleDataObjectOne:
             field_a = attr.ib()