Detailed assert failure introspection for attrs and dataclasses objects

.gitignore

@@ -44,3 +44,4 @@ coverage.xml
 .pydevproject
 .project
 .settings
+.vscode

AUTHORS

@@ -11,6 +11,7 @@ Alan Velasco
 Alexander Johnson
 Alexei Kozlenok
 Allan Feldman
+Aly Sivji
 Anatoly Bubenkoff
 Anders Hovmöller
 Andras Tim

changelog/3632.feature.rst

@@ -0,0 +1 @@
+Richer equality 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+, `backported to 3.6 <https://pypi.org/project/dataclasses>`_).

doc/en/example/assertion/failure_demo.py

@@ -101,6 +101,30 @@ def test_not_in_text_single_long_term(self):
         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

@@ -122,6 +122,12 @@ def isdict(x):
     def isset(x):
         return isinstance(x, (set, frozenset))
 
+    def isdatacls(obj):
+        return getattr(obj, "__dataclass_fields__", None) is not None
+
+    def isattrs(obj):
+        return getattr(obj, "__attrs_attrs__", None) is not None
+
     def isiterable(obj):
         try:
             iter(obj)
@@ -142,6 +148,9 @@ def isiterable(obj):
                     explanation = _compare_eq_set(left, right, verbose)
                 elif isdict(left) and isdict(right):
                     explanation = _compare_eq_dict(left, right, verbose)
+                elif type(left) == type(right) and (isdatacls(left) or isattrs(left)):
+                    type_fn = (isdatacls, isattrs)
+                    explanation = _compare_eq_cls(left, right, verbose, type_fn)
                 if isiterable(left) and isiterable(right):
                     expl = _compare_eq_iterable(left, right, verbose)
                     if explanation is not None:
@@ -315,6 +324,38 @@ def _compare_eq_dict(left, right, verbose=False):
     return explanation
 
 
+def _compare_eq_cls(left, right, verbose, type_fns):
+    isdatacls, isattrs = type_fns
+    if isdatacls(left):
+        all_fields = left.__dataclass_fields__
+        fields_to_check = [field for field, info in all_fields.items() if info.compare]
+    elif isattrs(left):
+        all_fields = left.__attrs_attrs__
+        fields_to_check = [field.name for field in all_fields if field.cmp]
+
+    same = []
+    diff = []
+    for field in fields_to_check:
+        if getattr(left, field) == getattr(right, field):
+            same.append(field)
+        else:
+            diff.append(field)
+
+    explanation = []
+    if same and verbose < 2:
+        explanation.append(u"Omitting %s identical items, use -vv to show" % len(same))
+    elif same:
+        explanation += [u"Matching attributes:"]
+        explanation += pprint.pformat(same).splitlines()
+    if diff:
+        explanation += [u"Differing attributes:"]
+        for field in diff:
+            explanation += [
+                (u"%s: %r != %r") % (field, getattr(left, field), getattr(right, field))
+            ]
+    return explanation
+
+
 def _notin_text(term, text, verbose=False):
     index = text.find(term)
     head = text[:index]

testing/example_scripts/dataclasses/test_compare_dataclasses.py

@@ -0,0 +1,14 @@
+from dataclasses import dataclass
+from dataclasses import field
+
+
+def test_dataclasses():
+    @dataclass
+    class SimpleDataObject(object):
+        field_a: int = field()
+        field_b: int = field()
+
+    left = SimpleDataObject(1, "b")
+    right = SimpleDataObject(1, "c")
+
+    assert left == right

testing/example_scripts/dataclasses/test_compare_dataclasses_field_comparison_off.py

@@ -0,0 +1,14 @@
+from dataclasses import dataclass
+from dataclasses import field
+
+
+def test_dataclasses_with_attribute_comparison_off():
+    @dataclass
+    class SimpleDataObject(object):
+        field_a: int = field()
+        field_b: int = field(compare=False)
+
+    left = SimpleDataObject(1, "b")
+    right = SimpleDataObject(1, "c")
+
+    assert left == right

testing/example_scripts/dataclasses/test_compare_dataclasses_verbose.py

@@ -0,0 +1,14 @@
+from dataclasses import dataclass
+from dataclasses import field
+
+
+def test_dataclasses_verbose():
+    @dataclass
+    class SimpleDataObject(object):
+        field_a: int = field()
+        field_b: int = field()
+
+    left = SimpleDataObject(1, "b")
+    right = SimpleDataObject(1, "c")
+
+    assert left == right

testing/example_scripts/dataclasses/test_compare_two_different_dataclasses.py

@@ -0,0 +1,19 @@
+from dataclasses import dataclass
+from dataclasses import field
+
+
+def test_comparing_two_different_data_classes():
+    @dataclass
+    class SimpleDataObjectOne(object):
+        field_a: int = field()
+        field_b: int = field()
+
+    @dataclass
+    class SimpleDataObjectTwo(object):
+        field_a: int = field()
+        field_b: int = field()
+
+    left = SimpleDataObjectOne(1, "b")
+    right = SimpleDataObjectTwo(1, "c")
+
+    assert left != right

testing/test_assertion.py

@@ -6,6 +6,7 @@
 import sys
 import textwrap
 
+import attr
 import py
 import six
 
@@ -548,6 +549,115 @@ def test_mojibake(self):
         assert msg
 
 
+class TestAssert_reprcompare_dataclass(object):
+    @pytest.mark.skipif(sys.version_info < (3, 7), reason="Dataclasses in Python3.7+")
+    def test_dataclasses(self, testdir):
+        p = testdir.copy_example("dataclasses/test_compare_dataclasses.py")
+        result = testdir.runpytest(p)
+        result.assert_outcomes(failed=1, passed=0)
+        result.stdout.fnmatch_lines(
+            [
+                "*Omitting 1 identical items, use -vv to show*",
+                "*Differing attributes:*",
+                "*field_b: 'b' != 'c'*",
+            ]
+        )
+
+    @pytest.mark.skipif(sys.version_info < (3, 7), reason="Dataclasses in Python3.7+")
+    def test_dataclasses_verbose(self, testdir):
+        p = testdir.copy_example("dataclasses/test_compare_dataclasses_verbose.py")
+        result = testdir.runpytest(p, "-vv")
+        result.assert_outcomes(failed=1, passed=0)
+        result.stdout.fnmatch_lines(
+            [
+                "*Matching attributes:*",
+                "*['field_a']*",
+                "*Differing attributes:*",
+                "*field_b: 'b' != 'c'*",
+            ]
+        )
+
+    @pytest.mark.skipif(sys.version_info < (3, 7), reason="Dataclasses in Python3.7+")
+    def test_dataclasses_with_attribute_comparison_off(self, testdir):
+        p = testdir.copy_example(
+            "dataclasses/test_compare_dataclasses_field_comparison_off.py"
+        )
+        result = testdir.runpytest(p, "-vv")
+        result.assert_outcomes(failed=0, passed=1)
+
+    @pytest.mark.skipif(sys.version_info < (3, 7), reason="Dataclasses in Python3.7+")
+    def test_comparing_two_different_data_classes(self, testdir):
+        p = testdir.copy_example(
+            "dataclasses/test_compare_two_different_dataclasses.py"
+        )
+        result = testdir.runpytest(p, "-vv")
+        result.assert_outcomes(failed=0, passed=1)
+
+
+class TestAssert_reprcompare_attrsclass(object):
+    def test_attrs(self):
+        @attr.s
+        class SimpleDataObject(object):
+            field_a = attr.ib()
+            field_b = attr.ib()
+
+        left = SimpleDataObject(1, "b")
+        right = SimpleDataObject(1, "c")
+
+        lines = callequal(left, right)
+        assert lines[1].startswith("Omitting 1 identical item")
+        assert "Matching attributes" not in lines
+        for line in lines[1:]:
+            assert "field_a" not in line
+
+    def test_attrs_verbose(self):
+        @attr.s
+        class SimpleDataObject(object):
+            field_a = attr.ib()
+            field_b = attr.ib()
+
+        left = SimpleDataObject(1, "b")
+        right = SimpleDataObject(1, "c")
+
+        lines = callequal(left, right, verbose=2)
+        assert lines[1].startswith("Matching attributes:")
+        assert "Omitting" not in lines[1]
+        assert lines[2] == "['field_a']"
+
+    def test_attrs_with_attribute_comparison_off(self):
+        @attr.s
+        class SimpleDataObject(object):
+            field_a = attr.ib()
+            field_b = attr.ib(cmp=False)
+
+        left = SimpleDataObject(1, "b")
+        right = SimpleDataObject(1, "b")
+
+        lines = callequal(left, right, verbose=2)
+        assert lines[1].startswith("Matching 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_two_different_attrs_classes(self):
+        @attr.s
+        class SimpleDataObjectOne(object):
+            field_a = attr.ib()
+            field_b = attr.ib()
+
+        @attr.s
+        class SimpleDataObjectTwo(object):
+            field_a = attr.ib()
+            field_b = attr.ib()
+
+        left = SimpleDataObjectOne(1, "b")
+        right = SimpleDataObjectTwo(1, "c")
+
+        lines = callequal(left, right)
+        assert lines is None
+
+
 class TestFormatExplanation(object):
     def test_special_chars_full(self, testdir):
         # Issue 453, for the bug this would raise IndexError

tox.ini

@@ -141,7 +141,7 @@ commands =
     sphinx-build -W -b html . _build
 
 [testenv:doctesting]
-basepython = python
+basepython = python3
 skipsdist = True
 deps =
     PyYAML