diff --git a/tests/skill/understand/test_merge_batch_graphs.py b/tests/skill/understand/test_merge_batch_graphs.py
index 33504f212..6be942ccc 100644
--- a/tests/skill/understand/test_merge_batch_graphs.py
+++ b/tests/skill/understand/test_merge_batch_graphs.py
@@ -132,6 +132,29 @@ def test_python_test_files(self) -> None:
         self.assertTrue(mbg.is_test_path("bar_test.py"))
         self.assertTrue(mbg.is_test_path("test_bar.py"))
 
+    def test_python_tests_directory(self) -> None:
+        # Files under `tests/` count as tests even without a `test_` prefix or
+        # `_test` suffix — e.g. `tests/run_tests.py`, `tests/stage4_e2e.py`.
+        for path in [
+            "tests/run_tests.py",
+            "tests/stage3_tests.py",
+            "tests/stage4_e2e.py",
+            "tests/gen_data.py",
+            "tests/helpers.py",
+        ]:
+            with self.subTest(path=path):
+                self.assertTrue(mbg.is_test_path(path), f"{path} should be a test")
+
+    def test_python_non_test_paths(self) -> None:
+        # A `tests` substring elsewhere in the path must not trigger a match.
+        for path in [
+            "data_agent/core/sqlite_utils.py",
+            "mypkg/testing/helpers.py",
+            "src/latest.py",
+        ]:
+            with self.subTest(path=path):
+                self.assertFalse(mbg.is_test_path(path), f"{path} should NOT be a test")
+
     def test_java_test_files(self) -> None:
         self.assertTrue(mbg.is_test_path("src/test/java/com/foo/BarTest.java"))
         self.assertTrue(mbg.is_test_path("src/test/java/com/foo/BarTests.java"))
diff --git a/understand-anything-plugin/skills/understand/merge-batch-graphs.py b/understand-anything-plugin/skills/understand/merge-batch-graphs.py
index b0cf51a3b..f8ef6b65a 100644
--- a/understand-anything-plugin/skills/understand/merge-batch-graphs.py
+++ b/understand-anything-plugin/skills/understand/merge-batch-graphs.py
@@ -130,7 +130,7 @@ def resolve_ua_dir(root: Path) -> Path:
 # These language configs treat every source file below `tests/` as part of a
 # test target, even when the basename itself has no test marker.  JS/TS is
 # intentionally absent: files such as `__tests__/helpers.ts` remain helpers.
-_TEST_DIRECTORY_EXTENSIONS: frozenset[str] = frozenset({".swift", ".rs", ".php"})
+_TEST_DIRECTORY_EXTENSIONS: frozenset[str] = frozenset({".swift", ".rs", ".php", ".py"})
 
 _EXACT_TEST_STEMS: dict[str, frozenset[str]] = {
     ".rb": frozenset({"spec_helper"}),
@@ -342,9 +342,11 @@ def _basename(path: str) -> str:
 def is_test_path(path: str) -> bool:
     """Return True if `path` looks like a test file by language convention.
 
-    Most languages use basename markers. Swift, Rust, and PHP additionally
-    make `tests/` a test-source root. JS/TS files still require `.test` or
-    `.spec`, so `__tests__/helpers.ts` remains a non-test helper.
+    Most languages use basename markers. Swift, Rust, PHP, and Python
+    additionally make `tests/` a test-source root, so `tests/run_tests.py`
+    (no `test_` prefix, no `_test` suffix) is still recognized as a test.
+    JS/TS files still require `.test` or `.spec`, so `__tests__/helpers.ts`
+    remains a non-test helper.
     """
     stem, ext = os.path.splitext(_basename(path))
     ext = ext.lower()