Full diff issue

AUTHORS

@@ -180,6 +180,7 @@ Jake VanderPlas
 Jakob van Santen
 Jakub Mitoraj
 James Bourbeau
+Jamie Chen
 Jan Balster
 Janne Vanhala
 Jason R. Coombs
@@ -206,6 +207,7 @@ Justice Ndou
 Justyna Janczyszyn
 Kale Kundert
 Kamran Ahmad
+Kaylin Yeoh
 Kenny Y
 Karl O. Pinc
 Karthikeyan Singaravelan

changelog/10863.bugfix.rst

@@ -0,0 +1,4 @@
+Found source causes multiline string diff error
+Added private functions to check specific cases
+Fixed output issue with implicit concatonated strings
+Added tests in test assertion file in function test_multiline_diff

src/_pytest/assertion/util.py

@@ -12,6 +12,7 @@
 from typing import Optional
 from typing import Protocol
 from typing import Sequence
+from typing import Tuple
 from unicodedata import normalize
 
 import _pytest._code
@@ -331,8 +332,17 @@
     # dynamic import to speedup pytest
     import difflib
 
-    left_formatting = PrettyPrinter().pformat(left).splitlines()
-    right_formatting = PrettyPrinter().pformat(right).splitlines()
+    if _is_empty_vs_non_empty(left, right):
+        left_formatting, right_formatting = _format_for_empty_and_non_empty(left, right)
+        lines_left = len(left_formatting)
+        lines_right = len(right_formatting)
+
+        if lines_left > 1 or lines_right > 1:
+            _surrounding_parens_on_own_lines(left_formatting)
+            _surrounding_parens_on_own_lines(right_formatting)
+    else:
+        left_formatting = PrettyPrinter().pformat(left).splitlines()
+        right_formatting = PrettyPrinter().pformat(right).splitlines()
 
     explanation = ["", "Full diff:"]
     # "right" is the expected base against which we compare "left",
@@ -349,6 +359,43 @@
     return explanation
 
 
+def _surrounding_parens_on_own_lines(lines: List[str]) -> None:
+    """Move opening/closing parenthesis/bracket to own lines."""
+    opening = lines[0][:1]
+    if opening in ["(", "[", "{"]:
+        lines[0] = " " + lines[0][1:]
+        lines[:] = [opening] + lines
+    closing = lines[-1][-1:]
+    if closing in [")", "]", "}"]:
+        lines[-1] = lines[-1][:-1] + ","
+        lines[:] = lines + [closing]
+
+
+def _is_empty_vs_non_empty(left: Iterable[Any], right: Iterable[Any]) -> bool:
+    is_left_empty = not any(left) if isinstance(left, Iterable) else not left
+    is_right_empty = not any(right) if isinstance(right, Iterable) else not right
+    return (is_left_empty and not is_right_empty) or (
+        not is_left_empty and is_right_empty
+    )
+
+
+def _format_for_empty_and_non_empty(
+    left: Iterable[Any], right: Iterable[Any]
+) -> Tuple[List[str], List[str]]:
+    if isinstance(left, (list, tuple)) and isinstance(right, (list, tuple)):
+        if not left:
+            right_width = max(len(s) + 4 for s in right)
+            right_formatting = pprint.pformat(right, width=right_width).splitlines()
+            left_formatting = pprint.pformat(left).splitlines()
+        else:
+            left_width = max(len(s) + 4 for s in left)
+            left_formatting = pprint.pformat(left, width=left_width).splitlines()
+            right_formatting = pprint.pformat(right).splitlines()
+        return left_formatting, right_formatting
+    else:
+        return pprint.pformat(left).splitlines(), pprint.pformat(right).splitlines()
+
+
 def _compare_eq_sequence(
     left: Sequence[Any], right: Sequence[Any], verbose: int = 0
 ) -> List[str]:

testing/test_assertion.py

@@ -397,6 +397,89 @@ def test_text_diff(self) -> None:
             "+ spam",
         ]
 
+    def test_multiline_diff(self) -> None:
+        m1 = [
+            "This is some dummy test which shows the strange way in which Pycharm"
+            " displays the full diff."
+        ]
+        m2 = [
+            "This is some dummy test which shows the strange way in which Pycharm"
+            " displays the full diff.This is some dummy test which shows the strange way in which Pycharm"
+            " displays the full diff."
+        ]
+        m3 = [
+            "This is some dummy test which shows the strange way in which Pycharm"
+            " displays the full diff.",
+            "This is some dummy test which shows the strange way in which Pycharm"
+            " displays the full diff.",
+        ]
+
+        assert callequal(m1, []) == [
+            "['This is som...e full diff.'] == []",
+            "",
+            "Left contains one more item: 'This is some dummy test which shows the "
+            "strange way in which Pycharm displays the full diff.'",
+            "Use -v to get more diff",
+        ]
+        assert callequal(m1, [], verbose=True) == [
+            "['This is som...e full diff.'] == []",
+            "",
+            "Left contains one more item: 'This is some dummy test which shows the "
+            "strange way in which Pycharm displays the full diff.'",
+            "",
+            "Full diff:",
+            "- []",
+            "+ ['This is some dummy test which shows the strange way in which Pycharm "
+            "displays the full diff.']",
+        ]
+
+        assert callequal(m2, []) == [
+            "['This is som...e full diff.'] == []",
+            "",
+            "Left contains one more item: 'This is some dummy test which shows the "
+            "strange way in which Pycharm displays the full diff.This is some dummy test "
+            "which shows the strange way in which Pycharm displays the full diff.'",
+            "Use -v to get more diff",
+        ]
+
+        assert callequal(m2, [], verbose=True) == [
+            "['This is som...e full diff.'] == []",
+            "",
+            "Left contains one more item: 'This is some dummy test which shows the "
+            "strange way in which Pycharm displays the full diff.This is some dummy test "
+            "which shows the strange way in which Pycharm displays the full diff.'",
+            "" "",
+            "Full diff:",
+            "- []",
+            "+ ['This is some dummy test which shows the strange way in which Pycharm "
+            "displays the full diff.This is some dummy test which shows the strange "
+            "way in which Pycharm displays the full diff.']",
+        ]
+
+        assert callequal(m3, []) == [
+            "['This is som...e full diff.'] == []",
+            "",
+            "Left contains 2 more items, first extra item: 'This is some dummy test which shows the strange way in "
+            "which Pycharm displays the full diff.'",
+            "" "Use -v to get more diff",
+        ]
+
+        assert callequal(m3, [], verbose=True) == [
+            "['This is som...e full diff.'] == []",
+            "",
+            "Left contains 2 more items, first extra item: 'This is some dummy test which shows the strange way in "
+            "which Pycharm displays the full diff.'",
+            "",
+            "Full diff:",
+            "  [",
+            "-  ,",
+            "+  'This is some dummy test which shows the strange way in which Pycharm "
+            "displays the full diff.',",
+            "+  'This is some dummy test which shows the strange way in which Pycharm "
+            "displays the full diff.',",
+            "  ]",
+        ]
+
     def test_text_skipping(self) -> None:
         lines = callequal("a" * 50 + "spam", "a" * 50 + "eggs")
         assert lines is not None