Add regression tests for issue pylint-dev#3711

tests/functional/u/undefined/undefined_loop_variable.py

@@ -73,3 +73,33 @@ def range(key):
     for var in range(3):
         pass
     return var # [undefined-loop-variable]
+
+
+def test(content):
+    # https://github.com/PyCQA/pylint/issues/3711
+    def handle_line(layne):
+        if "X" in layne:
+            layne = layne.replace("X", "Y")
+        elif "Y" in layne:  # line 5
+            layne = '{}'.format(layne)
+        elif "Z" in layne:  # line 7
+            layne = f'{layne}'
+        else:
+            layne = '%s' % layne  # line 10
+
+    for layne in content.split('\n'):
+        handle_line(layne)
+
+
+lst = []
+lst2 = [1, 2, 3]
+
+for item in lst:
+    pass
+
+bigger = [
+    [
+        x for x in lst2 if x > item
+    ]
+    for item in lst
+]