Question

I am trying to test if the parameters passed to an interface are correct:

MailMessage expectedMailMessage = new MailMessage();

var mailerMock = new Mock<IMailSender>();
mailerMock.Setup(m => m.Send(expectedMailMessage)).Verifiable();

Mailer mailer = new Mailer(mailerMock.Object);
mailer.Send(expectedMailMessage);

mailerMock.Verify(m => m.Send(expectedMailMessage), Times.Once());

Mailer class:

public class Mailer : IMailer
{
    private readonly IMailSender _mailSender;
    public Mailer(IMailSender mailSender)
    {
        _mailSender = mailSender;
    }

    public void Send(MailMessage mailMessage)
    {
        _mailSender.Send(mailMessage);
    }
}

But still this fails, problem is that it is very hard to debug. I checked if there is some random Guid generated or a date is set, but I couldn’t find anything.

Answer 1

After some fiddling I gave up and come up with this:

mailerMock.Verify(m => m.Send(It.Is<MailMessage>(msg => msg.Subject == expectedMailMessage.Subject));
mailerMock.Verify(m => m.Send(It.Is<MailMessage>(msg => msg.Sender == expectedMailMessage.Sender));

Also easier to see on which property it is failing.