Add test for #1604: allow toggling section header in indented imports

tests/unit/test_ticketed_features.py

@@ -923,3 +923,51 @@ def one():
 import os
 """
     )
+
+
+def test_indented_import_headings_issue_1604():
+    """Test to ensure it is possible to toggle import headings on indented import sections
+    See: https://github.com/PyCQA/isort/issues/1604
+    """
+    assert (
+        isort.code(
+            """
+import numpy as np
+
+
+def function():
+    import numpy as np
+""",
+            import_heading_thirdparty="External imports",
+        )
+        == """
+# External imports
+import numpy as np
+
+
+def function():
+    # External imports
+    import numpy as np
+"""
+    )
+    assert (
+        isort.code(
+            """
+import numpy as np
+
+
+def function():
+    import numpy as np
+""",
+            import_heading_thirdparty="External imports",
+            indented_import_headings=False,
+        )
+        == """
+# External imports
+import numpy as np
+
+
+def function():
+    import numpy as np
+"""
+    )