start writing test

Author: MarcoGorelli

tests/no_single_letter_variables_test.py

@@ -0,0 +1,45 @@
+import ast
+import tokenize
+from io import StringIO
+
+import pytest
+
+from pandas_dev_flaker.__main__ import run
+
+
+def results(s):
+    return {
+        "{}:{}: {}".format(*r)
+        for r in run(
+            ast.parse(s),
+            list(tokenize.generate_tokens(StringIO(s).readline)),
+        )
+    }
+
+
+@pytest.mark.parametrize(
+    "source",
+    (
+        pytest.param(
+            "ab = 3",
+            id="Multi-letter assignment",
+        ),
+    ),
+)
+def test_noop(source):
+    assert not results(source)
+
+
+@pytest.mark.parametrize(
+    "source, expected",
+    (
+        pytest.param(
+            "a = 3",
+            "1:0: PDF023 don't assign to single-letter variables",
+            id="Single letter variable",
+        ),
+    ),
+)
+def test_violation(source, expected):
+    (result,) = results(source)
+    assert result == expected