Strange exception testing EmailSender - asp.net

Question

I have just closely followed all MS instructions on scaffolding the Identity UI in an ASP.NET Core 3.0 MVC app. If I run the project, it opens the default home page fine, and links on that page respond well. Yet a simple integration test fails with an exception.
The single method in the EmailSender looks like this:
public Task SendEmailAsync(string email, string subject, string htmlMessage)
{
using (var client = new SmtpClient())
using (var msg = new MailMessage())
{
msg.From = new MailAddress("system#timekeeper.co.za");
msg.To.Add(new MailAddress(email));
msg.Subject = subject;
msg.IsBodyHtml = true;
client.UseDefaultCredentials = false;
client.Credentials = new NetworkCredential("timekeeper#somewhere.com", "something");
client.Host = "mail.myhost.com";
client.Port = 25;
return client.SendMailAsync(msg);
}
}
and my test looks like this:
[TestMethod]
public async Task Send_Email()
{
var sender = new EmailSender();
await sender.SendEmailAsync("somebody#somewhere.net", "Test Mail", "This is a test");
Assert.IsTrue(true);
}
When I run the test it fails with the following exception:
Test method TimeKeeper.Tests.Integration.EmailSEnderTests.Send_Email threw exception:
System.Threading.Tasks.TaskCanceledException: A task was canceled.
at TimeKeeper.Tests.Integration.EmailSEnderTests.Send_Email() in D:\Dev\RestServices\TimeKeeper.Tests.Integration\EmailSEnderTests.cs:line 15
at Microsoft.VisualStudio.TestPlatform.MSTestAdapter.PlatformServices.ThreadOperations.ExecuteWithAbortSafety(Action action)

Answer 1

await the task instead of returning it.
public async Task SendEmailAsync(string email, string subject, string htmlMessage) {
using (var client = new SmtpClient())
using (var msg = new MailMessage()) {
msg.From = new MailAddress("system#timekeeper.co.za");
msg.To.Add(new MailAddress(email));
msg.Subject = subject;
msg.IsBodyHtml = true;
client.UseDefaultCredentials = false;
client.Credentials = new NetworkCredential("timekeeper#somewhere.com", "something");
client.Host = "mail.myhost.com";
client.Port = 25;
await client.SendMailAsync(msg); //<-- await completion
}
}
Chances are that the client is being disposed before it has a chance to complete sending the email.
You should also take note of the warnings in documentation about using the now obsolete SmtpClient for new development.
DE0005: SmtpClient shouldn't be used
Motivation
SmtpClient doesn't support many modern protocols. It is compat-only. It's great for one off emails from tools, but doesn't
scale to modern requirements of the protocol.
Recommendation
Use MailKit or other libraries.