Add test data

tests/code.py

@@ -0,0 +1,10 @@
+from typing import Optional
+
+
+def code(arg: Optional[bool]) -> str:
+    if arg is None:
+        return "a"
+    elif arg is True:
+        return "b"
+    else:
+        return "c"

tests/requirements.txt

@@ -0,0 +1,2 @@
+pytest
+pytest-cov

tests/test_code.py

@@ -0,0 +1,8 @@
+import pytest
+
+from . import code
+
+
+@pytest.mark.parametrize("arg, expected", [(None, "a")])
+def test_code(arg, expected):
+    assert code.code(arg) == expected