Add tests against environment pollution

Author: krassowski

jupyterlab_code_formatter/tests/test_formatters.py

@@ -0,0 +1,38 @@
+import json
+import os
+import sys
+from subprocess import run
+from unittest import mock
+
+import pytest
+
+from jupyterlab_code_formatter.formatters import SERVER_FORMATTERS
+
+
+def test_env_pollution_on_import():
+    # should not pollute environment on import
+    code = "; ".join(
+        [
+            "from jupyterlab_code_formatter import formatters",
+            "import json",
+            "import os",
+            "assert formatters",
+            "print(json.dumps(os.environ.copy()))",
+        ]
+    )
+    result = run([sys.executable, "-c", f"{code}"], capture_output=True, text=True, check=True, env={})
+    environ = json.loads(result.stdout)
+    assert set(environ.keys()) - {"LC_CTYPE"} == set()
+
+
+@pytest.mark.parametrize("name", SERVER_FORMATTERS)
+def test_env_pollution_on_importable_check(name):
+    formatter = SERVER_FORMATTERS[name]
+    # should not pollute environment on `importable` check
+    with mock.patch.dict(os.environ, {}, clear=True):
+        # invoke the property getter
+        is_importable = formatter.importable
+        # the environment should have no extra keys
+        assert set(os.environ.keys()) == set()
+        if not is_importable:
+            pytest.skip(f"{name} formatter was not importable, the test may yield false negatives")