Ensure the docstring is a string

AUTHORS

@@ -373,6 +373,7 @@ Tomer Keren
 Tony Narlock
 Tor Colvin
 Trevor Bekolay
+Tushar Sadhwani
 Tyler Goodlet
 Tzu-ping Chung
 Vasily Kuznetsov

changelog/11146.bugfix.rst

@@ -0,0 +1 @@
+- Prevent constants at the top of file from being detected as docstrings.

src/_pytest/assertion/rewrite.py

@@ -676,6 +676,7 @@ def run(self, mod: ast.Module) -> None:
                 expect_docstring
                 and isinstance(item, ast.Expr)
                 and isinstance(item.value, ast.Constant)
+                and isinstance(item.value.value, str)
             ):
                 doc = item.value.value
                 if self.is_rewrite_disabled(doc):

testing/test_assertrewrite.py

@@ -2042,3 +2042,17 @@ def test_max_increased_verbosity(self, pytester: Pytester) -> None:
         self.create_test_file(pytester, DEFAULT_REPR_MAX_SIZE * 10)
         result = pytester.runpytest("-vv")
         result.stdout.no_fnmatch_line("*xxx...xxx*")
+
+
+class TestIssue11140:
+    def test_constant_not_picked_as_module_docstring(self, pytester: Pytester) -> None:
+        pytester.makepyfile(
+            """\
+            0
+
+            def test_foo():
+                pass
+            """
+        )
+        result = pytester.runpytest()
+        assert result.ret == 0