def METHOD_NAME(aws_accounts):
    existing_groups = [
        {
            "group_name": "bar",
            "expires_at": "tomorrow",
        }
    ]
    existing_properties = UserProperties(
        user_name="foo",
        groups=existing_groups,
    )
    new_groups = [
        {
            "group_name": "baz",
        },
        {
            "group_name": "bar",
        },
    ]
    new_properties = UserProperties(
        user_name="foo",
        groups=new_groups,
    )
    merged_properties: UserProperties = merge_model(
        new_properties, existing_properties, aws_accounts
    )
    assert merged_properties.groups[0].group_name == "bar"
    assert (
        merged_properties.groups[0].expires_at
        == existing_properties.groups[0].expires_at
    )
    assert merged_properties.groups[1].group_name == "baz"