Index: flake8_pyi-23.1.2/tests/test_pyi_files.py
===================================================================
--- flake8_pyi-23.1.2.orig/tests/test_pyi_files.py
+++ flake8_pyi-23.1.2/tests/test_pyi_files.py
@@ -35,16 +35,21 @@ def test_pyi_file(path: str) -> None:
             message = line[match.end() : end_pos].strip()
             expected_output += f"{path}:{lineno}: {match.group(1)}{message}\n"
 
+    pythonpath = os.environ.get("PYTHONPATH")
+    pythonpath = f"PYTHONPATH={pythonpath}:."
+
     run_results = [
         # Passing a file on command line
         subprocess.run(
-            ["flake8", "-j0", *flags, path],
+            " ".join([pythonpath, "flake8", "-j0", *flags, path]),
+            shell=True,
             env={**os.environ, "PYTHONPATH": "."},
             stdout=subprocess.PIPE,
         ),
         # Passing "-" as the file, and reading from stdin instead
         subprocess.run(
-            ["flake8", "-j0", "--stdin-display-name", path, *flags, "-"],
+            " ".join([pythonpath, "flake8", "-j0", "--stdin-display-name", path, *flags, "-"]),
+            shell=True,
             env={**os.environ, "PYTHONPATH": "."},
             input=file_contents.encode("utf-8"),
             stdout=subprocess.PIPE,