Pass actual exception to Assert.ThrowsException(Async) assertion error message builder about testfx

[Evangelink]

Hi @gao-artur,

Thanks for the suggestion. I am not sure to fully understand what you would like to be able to do. At the moment, all ThrowsExceptionAsync gives you a Task<TException> so awaiting that gives you your exception.

[gao-artur]

Hi @Evangelink. When thrown exception is different from the expected, it may be helpful to get the actual exception to create the error message. For example, you expect to get OperationCancellaedException, but RpcException is thrown instead. RpcException has a few properties with useful information, like Trailers for example. You would want to use this additional data in the error message (second argument in ThrowsExceptionAsync method). Currently, the framework will create an error message based on the user message, exception type, message, and stack trace.

if (!typeof(T).Equals(ex.GetType()))
{
    userMessage = BuildUserMessage(message, parameters);
    finalMessage = string.Format(
        CultureInfo.CurrentCulture,
        FrameworkMessages.WrongExceptionThrown,
        userMessage,
        typeof(T).Name,
        ex.GetType().Name,
        ex.Message,
        ex.StackTrace);
    ThrowAssertFailed("Assert.ThrowsException", finalMessage);
}

I suggest passing the exception to the user message builder. Note the Func<Exception?, string> messageBuilder instead of string message

public static async Task<T> ThrowsExceptionAsync<T>(Func<Task> action, Func<Exception?, string> messageBuilder, params object?[]? parameters)
    where T : Exception
{
    ...
    string userMessage, finalMessage;
    try
    {
        await action().ConfigureAwait(false);
    }
    catch (Exception ex)
    {
        if (!typeof(T).Equals(ex.GetType()))
        {
            userMessage = BuildUserMessage(messageBuilder, ex, parameters);
            ...
            ThrowAssertFailed("Assert.ThrowsException", finalMessage);
        }

        return (T)ex;
    }

    userMessage = BuildUserMessage(messageBuilder, exception: null, parameters);
    ...
    ThrowAssertFailed("Assert.ThrowsException", finalMessage);
    ...
}

Note the Func<Exception?, string> messageBuilder instead of string? format

internal static string BuildUserMessage(Func<Exception?, string> messageBuilder, Exception? exception, params object?[]? parameters)
{
    ...
    var format = messageBuilder(exception);

    return parameters == null || parameters.Length == 0
        ? ReplaceNulls(format)
        : string.Format(CultureInfo.CurrentCulture, ReplaceNulls(format), parameters);
}