From 3db9c6be2de00331c5f4e520d2822c0eb13c7280 Mon Sep 17 00:00:00 2001
From: Mike Bayer <mike_mp@zzzcomputing.com>
Date: Mon, 27 Oct 2025 10:56:49 -0400
Subject: [PATCH] try to improve coverage a bit

use pyproject.toml so the options are safe from "rm .coverage*"
types of commands

omit some files

add test coverage for a big section of cache-key

Change-Id: Ia540c632d91ec09284e187e3edeb8ccf0214e1a6
---
 .coveragerc              |  7 -----
 noxfile.py               |  4 +++
 pyproject.toml           | 13 ++++++++++
 test/sql/test_compare.py | 55 ++++++++++++++++++++++++++++++++++++++++
 4 files changed, 72 insertions(+), 7 deletions(-)
 delete mode 100644 .coveragerc

diff --git a/.coveragerc b/.coveragerc
deleted file mode 100644
index e279765ddf..0000000000
--- a/.coveragerc
+++ /dev/null
@@ -1,7 +0,0 @@
-[paths]
-source=lib/
-
-[run]
-relative_files=True
-
-
diff --git a/noxfile.py b/noxfile.py
index 6b593b06fb..a5afe31673 100644
--- a/noxfile.py
+++ b/noxfile.py
@@ -192,6 +192,10 @@ def _tests(
     timing_intensive: bool = True,
     coverage: bool = False,
 ) -> None:
+
+    # ensure external PYTHONPATH not interfering
+    session.env["PYTHONPATH"] = ""
+
     # PYTHONNOUSERSITE - this *MUST* be set so that the ./lib/ import
     # set up explicitly in test/conftest.py is *disabled*, so that
     # when SQLAlchemy is built into the .nox area, we use that and not the
diff --git a/pyproject.toml b/pyproject.toml
index caeaf47c6e..8179aa4832 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -196,6 +196,19 @@ mypy = [
 ]
 
 
+[tool.coverage.paths]
+source="lib/"
+
+[tool.coverage.run]
+relative_files = true
+omit = [
+    "lib/sqlalchemy/testing/plugin/*",
+    "lib/sqlalchemy/testing/fixtures/mypy.py",
+    "lib/sqlalchemy/testing/profiling.py",
+    "lib/sqlalchemy/util/tool_support.py",
+]
+
+
 [tool.setuptools]
 include-package-data = true
 
diff --git a/test/sql/test_compare.py b/test/sql/test_compare.py
index 774f9792f4..94f34ddfff 100644
--- a/test/sql/test_compare.py
+++ b/test/sql/test_compare.py
@@ -49,6 +49,7 @@ from sqlalchemy.sql.base import DialectKWArgs
 from sqlalchemy.sql.base import HasCacheKey
 from sqlalchemy.sql.base import SingletonConstant
 from sqlalchemy.sql.base import SyntaxExtension
+from sqlalchemy.sql.cache_key import CacheKey
 from sqlalchemy.sql.elements import _label_reference
 from sqlalchemy.sql.elements import _textual_label_reference
 from sqlalchemy.sql.elements import BindParameter
@@ -2315,3 +2316,57 @@ class TypesTest(fixtures.TestBase):
 
         eq_(c1, c2)
         ne_(c1, c3)
+
+
+class TestWhatsDifferentUtil(fixtures.TestBase):
+    """Test the CacheKey._whats_different() utility method
+
+    Note: The _whats_different() method has a limitation where it can only
+    properly handle nested tuple structures. It was designed to work with
+    real cache keys which are always nested tuples.
+    """
+
+    def test_nested_tuple_difference(self):
+        """Test difference detection in nested tuples"""
+        k1 = CacheKey(key=((1, (2, 3, 4), 5),), bindparams=[])
+        k2 = CacheKey(key=((1, (2, 7, 4), 5),), bindparams=[])
+
+        eq_(list(k1._whats_different(k2)), ["key[0][1][1]:  3 != 7"])
+
+    def test_deeply_nested_tuple_difference(self):
+        """Test difference detection in deeply nested tuples"""
+        k1 = CacheKey(key=((1, (2, (3, 4, 5), 6), 7),), bindparams=[])
+        k2 = CacheKey(key=((1, (2, (3, 9, 5), 6), 7),), bindparams=[])
+
+        eq_(list(k1._whats_different(k2)), ["key[0][1][1][1]:  4 != 9"])
+
+    def test_multiple_differences_nested(self):
+        """Test detection of multiple differences in nested structure"""
+        k1 = CacheKey(key=((1, (2, 3), 4),), bindparams=[])
+        k2 = CacheKey(key=((1, (5, 7), 4),), bindparams=[])
+
+        eq_(
+            list(k1._whats_different(k2)),
+            ["key[0][1][0]:  2 != 5", "key[0][1][1]:  3 != 7"],
+        )
+
+    def test_diff_method(self):
+        """Test the _diff() method that returns a comma-separated string"""
+        k1 = CacheKey(key=((1, (2, 3)),), bindparams=[])
+        k2 = CacheKey(key=((1, (5, 7)),), bindparams=[])
+
+        eq_(k1._diff(k2), "key[0][1][0]:  2 != 5, key[0][1][1]:  3 != 7")
+
+    def test_with_string_differences(self):
+        """Test detection of string differences"""
+        k1 = CacheKey(key=(("name", ("x", "value")),), bindparams=[])
+        k2 = CacheKey(key=(("name", ("y", "value")),), bindparams=[])
+
+        eq_(list(k1._whats_different(k2)), ["key[0][1][0]:  x != y"])
+
+    def test_with_mixed_types(self):
+        """Test detection of differences with mixed types"""
+        k1 = CacheKey(key=(("id", 1, ("nested", 100)),), bindparams=[])
+        k2 = CacheKey(key=(("id", 1, ("nested", 200)),), bindparams=[])
+
+        eq_(list(k1._whats_different(k2)), ["key[0][2][1]:  100 != 200"])
-- 
2.47.3