Add regression test for issue #1264 demonstrating failure

tests/test_regressions.py

@@ -0,0 +1,14 @@
+"""A growing set of tests designed to ensure isort doesn't have regressions in new versions"""
+import isort
+
+
+def test_isort_duplicating_comments_issue_1264():
+    """Ensure isort doesn't duplicate comments when force_sort_within_sections is set to `True`
+    as was the case in issue #1264: https://github.com/timothycrosley/isort/issues/1264
+    """
+    assert isort.code("""
+from homeassistant.util.logging import catch_log_exception
+
+# Loading the config flow file will register...
+from . import config_flow
+""", force_sort_within_sections=True).count("# Loading the config flow file will register...") == 1