assertion: improve diff output of recursive dataclass/attrs

Co-authored-by: Vlad <uladzislau.radziuk@nordcloud.com>

AUTHORS

@@ -293,6 +293,7 @@ Vidar T. Fauske
 Virgil Dupras
 Vitaly Lashmanov
 Vlad Dragos
+Vlad Radziuk
 Vladyslav Rachek
 Volodymyr Piskun
 Wei Lin

changelog/7348.improvement.rst

@@ -0,0 +1 @@
+Improve recursive diff report for comparison asserts on dataclasses / attrs.

src/_pytest/assertion/util.py

@@ -169,7 +169,7 @@ def assertrepr_compare(config, op: str, left: Any, right: Any) -> Optional[List[
 
 
 def _compare_eq_any(left: Any, right: Any, verbose: int = 0) -> List[str]:
-    explanation = []  # type: List[str]
+    explanation = []
     if istext(left) and istext(right):
         explanation = _diff_text(left, right, verbose)
     else:
@@ -424,6 +424,7 @@ def _compare_eq_cls(
             field.name for field in all_fields if getattr(field, ATTRS_EQ_FIELD)
         ]
 
+    indent = "  "
     same = []
     diff = []
     for field in fields_to_check:
@@ -433,6 +434,8 @@ def _compare_eq_cls(
             diff.append(field)
 
     explanation = []
+    if same or diff:
+        explanation += [""]
     if same and verbose < 2:
         explanation.append("Omitting %s identical items, use -vv to show" % len(same))
     elif same:
@@ -440,12 +443,18 @@ def _compare_eq_cls(
         explanation += pprint.pformat(same).splitlines()
     if diff:
         explanation += ["Differing attributes:"]
+        explanation += pprint.pformat(diff).splitlines()
         for field in diff:
+            field_left = getattr(left, field)
+            field_right = getattr(right, field)
             explanation += [
-                ("%s: %r != %r") % (field, getattr(left, field), getattr(right, field)),
                 "",
                 "Drill down into differing attribute %s:" % field,
-                *_compare_eq_any(getattr(left, field), getattr(right, field), verbose),
+                ("%s%s: %r != %r") % (indent, field, field_left, field_right),
+            ]
+            explanation += [
+                indent + line
+                for line in _compare_eq_any(field_left, field_right, verbose)
             ]
     return explanation
 

testing/example_scripts/dataclasses/test_compare_recursive_dataclasses.py

@@ -1,34 +1,38 @@
 from dataclasses import dataclass
-from dataclasses import field
 
 
 @dataclass
-class SimpleDataObject:
+class S:
-    field_a: int = field()
+    a: int
-    field_b: str = field()
+    b: str
 
 
 @dataclass
-class ComplexDataObject2:
+class C:
-    field_a: SimpleDataObject = field()
+    c: S
-    field_b: SimpleDataObject = field()
+    d: S
 
 
 @dataclass
-class ComplexDataObject:
+class C2:
-    field_a: SimpleDataObject = field()
+    e: C
-    field_b: ComplexDataObject2 = field()
+    f: S
+
+
+@dataclass
+class C3:
+    g: S
+    h: C2
+    i: str
+    j: str
 
 
 def test_recursive_dataclasses():
-
+    left = C3(
-    left = ComplexDataObject(
+        S(10, "ten"), C2(C(S(1, "one"), S(2, "two")), S(2, "three")), "equal", "left",
-        SimpleDataObject(1, "b"),
-        ComplexDataObject2(SimpleDataObject(1, "b"), SimpleDataObject(2, "c"),),
     )
-    right = ComplexDataObject(
+    right = C3(
-        SimpleDataObject(1, "b"),
+        S(20, "xxx"), C2(C(S(1, "one"), S(2, "yyy")), S(3, "three")), "equal", "right",
-        ComplexDataObject2(SimpleDataObject(1, "b"), SimpleDataObject(3, "c"),),
     )
 
     assert left == right

testing/test_assertion.py

@@ -778,12 +778,16 @@ class TestAssert_reprcompare_dataclass:
         result.assert_outcomes(failed=1, passed=0)
         result.stdout.fnmatch_lines(
             [
-                "*Omitting 1 identical items, use -vv to show*",
+                "E         Omitting 1 identical items, use -vv to show",
-                "*Differing attributes:*",
+                "E         Differing attributes:",
-                "*field_b: 'b' != 'c'*",
+                "E         ['field_b']",
-                "*- c*",
+                "E         ",
-                "*+ b*",
+                "E         Drill down into differing attribute field_b:",
-            ]
+                "E           field_b: 'b' != 'c'...",
+                "E         ",
+                "E         ...Full output truncated (3 lines hidden), use '-vv' to show",
+            ],
+            consecutive=True,
         )
 
     @pytest.mark.skipif(sys.version_info < (3, 7), reason="Dataclasses in Python3.7+")
@@ -793,14 +797,16 @@ class TestAssert_reprcompare_dataclass:
         result.assert_outcomes(failed=1, passed=0)
         result.stdout.fnmatch_lines(
             [
-                "*Omitting 1 identical items, use -vv to show*",
+                "E         Omitting 1 identical items, use -vv to show",
-                "*Differing attributes:*",
+                "E         Differing attributes:",
-                "*field_b: ComplexDataObject2(*SimpleDataObject(field_a=2, field_b='c')) != ComplexDataObject2(*SimpleDataObject(field_a=3, field_b='c'))*",  # noqa
+                "E         ['g', 'h', 'j']",
-                "*Drill down into differing attribute field_b:*",
+                "E         ",
-                "*Omitting 1 identical items, use -vv to show*",
+                "E         Drill down into differing attribute g:",
-                "*Differing attributes:*",
+                "E           g: S(a=10, b='ten') != S(a=20, b='xxx')...",
-                "*Full output truncated*",
+                "E         ",
-            ]
+                "E         ...Full output truncated (52 lines hidden), use '-vv' to show",
+            ],
+            consecutive=True,
         )
 
     @pytest.mark.skipif(sys.version_info < (3, 7), reason="Dataclasses in Python3.7+")
@@ -810,19 +816,30 @@ class TestAssert_reprcompare_dataclass:
         result.assert_outcomes(failed=1, passed=0)
         result.stdout.fnmatch_lines(
             [
-                "*Matching attributes:*",
+                "E         Matching attributes:",
-                "*['field_a']*",
+                "E         ['i']",
-                "*Differing attributes:*",
+                "E         Differing attributes:",
-                "*field_b: ComplexDataObject2(*SimpleDataObject(field_a=2, field_b='c')) != ComplexDataObject2(*SimpleDataObject(field_a=3, field_b='c'))*",  # noqa
+                "E         ['g', 'h', 'j']",
-                "*Matching attributes:*",
+                "E         ",
-                "*['field_a']*",
+                "E         Drill down into differing attribute g:",
-                "*Differing attributes:*",
+                "E           g: S(a=10, b='ten') != S(a=20, b='xxx')",
-                "*field_b: SimpleDataObject(field_a=2, field_b='c') != SimpleDataObject(field_a=3, field_b='c')*",  # noqa
+                "E           ",
-                "*Matching attributes:*",
+                "E           Differing attributes:",
-                "*['field_b']*",
+                "E           ['a', 'b']",
-                "*Differing attributes:*",
+                "E           ",
-                "*field_a: 2 != 3",
+                "E           Drill down into differing attribute a:",
-            ]
+                "E             a: 10 != 20",
+                "E             +10",
+                "E             -20",
+                "E           ",
+                "E           Drill down into differing attribute b:",
+                "E             b: 'ten' != 'xxx'",
+                "E             - xxx",
+                "E             + ten",
+                "E         ",
+                "E         Drill down into differing attribute h:",
+            ],
+            consecutive=True,
         )
 
     @pytest.mark.skipif(sys.version_info < (3, 7), reason="Dataclasses in Python3.7+")
@@ -868,9 +885,9 @@ class TestAssert_reprcompare_attrsclass:
 
         lines = callequal(left, right)
         assert lines is not None
-        assert lines[1].startswith("Omitting 1 identical item")
+        assert lines[2].startswith("Omitting 1 identical item")
         assert "Matching attributes" not in lines
-        for line in lines[1:]:
+        for line in lines[2:]:
             assert "field_a" not in line
 
     def test_attrs_recursive(self) -> None:
@@ -910,7 +927,8 @@ class TestAssert_reprcompare_attrsclass:
 
         lines = callequal(left, right)
         assert lines is not None
-        assert "field_d: 'a' != 'b'" in lines
+        # indentation in output because of nested object structure
+        assert "    field_d: 'a' != 'b'" in lines
 
     def test_attrs_verbose(self) -> None:
         @attr.s
@@ -923,9 +941,9 @@ class TestAssert_reprcompare_attrsclass:
 
         lines = callequal(left, right, verbose=2)
         assert lines is not None
-        assert lines[1].startswith("Matching attributes:")
+        assert lines[2].startswith("Matching attributes:")
-        assert "Omitting" not in lines[1]
+        assert "Omitting" not in lines[2]
-        assert lines[2] == "['field_a']"
+        assert lines[3] == "['field_a']"
 
     def test_attrs_with_attribute_comparison_off(self):
         @attr.s
@@ -937,11 +955,12 @@ class TestAssert_reprcompare_attrsclass:
         right = SimpleDataObject(1, "b")
 
         lines = callequal(left, right, verbose=2)
+        print(lines)
         assert lines is not None
-        assert lines[1].startswith("Matching attributes:")
+        assert lines[2].startswith("Matching attributes:")
         assert "Omitting" not in lines[1]
-        assert lines[2] == "['field_a']"
+        assert lines[3] == "['field_a']"
-        for line in lines[2:]:
+        for line in lines[3:]:
             assert "field_b" not in line
 
     def test_comparing_two_different_attrs_classes(self):

testing/test_error_diffs.py

@@ -233,7 +233,11 @@ if sys.version_info[:2] >= (3, 7):
                 E         Matching attributes:
                 E         ['b']
                 E         Differing attributes:
-                E         a: 1 != 2
+                E         ['a']
+                E         Drill down into differing attribute a:
+                E           a: 1 != 2
+                E           +1
+                E           -2
                 """,
                 id="Compare data classes",
             ),
@@ -257,7 +261,11 @@ if sys.version_info[:2] >= (3, 7):
                 E         Matching attributes:
                 E         ['a']
                 E         Differing attributes:
-                E         b: 'spam' != 'eggs'
+                E         ['b']
+                E         Drill down into differing attribute b:
+                E           b: 'spam' != 'eggs'
+                E           - eggs
+                E           + spam
                 """,
                 id="Compare attrs classes",
             ),