TEMPLATE-ERROR Error {
    kind: Msg(
        "Failed to render 'content.html'",
    ),
    source: Some(
        Error {
            kind: CallTest(
                "containing",
            ),
            source: Some(
                Error {
                    kind: Msg(
                        "Tester `containing` was called with a parameter that isn't a string",
                    ),
                    source: None,
                },
            ),
        },
    ),
}