def METHOD_NAME():
    """Validate flatten_dict can handle nested dictionaries and argparse Namespace."""
    # Test basic dict flattening with custom delimiter
    params = {"a": {"b": "c"}}
    params = _flatten_dict(params, "--")
    assert "a" not in params
    assert params["a--b"] == "c"
    # Test complex nested dict flattening
    params = {"a": {5: {"foo": "bar"}}, "b": 6, "c": {7: [1, 2, 3, 4], 8: "foo", 9: {10: "bar"}}}
    params = _flatten_dict(params)
    assert "a" not in params
    assert params["a/5/foo"] == "bar"
    assert params["b"] == 6
    assert params["c/7"] == [1, 2, 3, 4]
    assert params["c/8"] == "foo"
    assert params["c/9/10"] == "bar"
    # Test flattening of argparse Namespace
    params = Namespace(a=1, b=2)
    wrapping_dict = {"params": params}
    params = _flatten_dict(wrapping_dict)
    assert type(params) == dict
    assert params["params/a"] == 1
    assert params["params/b"] == 2
    assert "a" not in params
    assert "b" not in params