BuildQuery.cs

private static QueryTest BuildQuery(string type, TArguments args, IEnumerable<string> fields)
{
    var arguments = args == null ? "" : GetArguments(args);
    var query = $"{{{type}{arguments}{{{string.Join(' ', fields)}}}}}";
    return new QueryTest(query);
}
 
private static string GetArguments(TArguments args)
{
    var values = args.GetType()
        .GetFields()
        .Select(x => new { name = x.Name, value = x.GetValue(args) })
        .Where(x => x.value != null)
        .Select(x => $"{x.name}:{FormatArgument(x.value)}");
    return $"({string.Join(',', values)})";
}

private static string FormatArgument(object value) =>
    value is string
        ? $"\"{value}\""
        : $"{value}"