[#34] add a third option: neither black nor autopep8

Signed-off-by: Bryant Finney <[email protected]>

pipenv_setup/setup_updater.py

@@ -5,7 +5,8 @@
 from io import BytesIO
 from subprocess import PIPE, Popen
 from tokenize import OP
-from typing import Any, List, Tuple
+from types import ModuleType
+from typing import Any, List, Optional, Tuple
 
 from vistir.compat import Path
 
@@ -149,11 +150,14 @@ def _get_formatting_module():  # type: () -> Optional[ModuleType]
     try:
         import black
     except:
-        import autopep8
 
+        try:
+            import autopep8
+        except ImportError:
+            return None
         return autopep8
-    else:
-        return black
+
+    return black
 
 
 def format_file(file):  # type: (Path) -> None

tests/setup_updater_test.py

@@ -101,3 +101,13 @@ def test_autopep8(monkeypatch, dummy_import):  # type: (MonkeyPatch, Callable) -
     is_autopep8 = setup_updater._get_formatting_module()
 
     assert is_autopep8 is autopep8
+
+
+def test_none(monkeypatch, extra_dummy_import):  # type: (MonkeyPatch, Callable) -> None
+    """
+    verify `None` is returned if neither `black` nor `autopep8` is present
+    """
+    patch_import(monkeypatch, extra_dummy_import)
+    is_none = setup_updater._get_formatting_module()
+
+    assert is_none is None