Can I register a fake instance and declare it's return on registration?

Question

I'm building a testing framework for our Xunit tests. I wanted to create a fake SMTP service that will mimic ours but won't actually work for the tests (For obvious reasons).

Creating a fake instance was easy and worked like a charm. I've added before the modules my the registration of the fakeItEasyObject:

builder.RegisterInstance(A.Fake<IEmailSender>());

but now I want it to ALWAYS return true on EmailSender.Send() , and I know I can achieve it from the actual unitests with the resolved instance: A.CallTo(()=>_emailSender.Send(A<Data>.Ignored)).Returns(true);

I don't want to do it on every test and was wondering if there is a way form to do it on registration. Do you know a way to do it?

Answer 1

Unless you're repeating your registration all over the place, you could just

var fake = A.Fake<IEmailSender>();
A.CallTo(() => fake.Send(A<Data>.Ignored))).Returns(true);
builder.RegisterInstance(fake);

But I suspect that's not what you're asking.

If you want the default for all your fakes to return true on Send, you could use FakeItEasy's Implicit Creation Options. Specifically an IFakeOptionsBuilder. Something like

public class EmailSenderFakeOptionsBuilder : FakeOptionsBuilder<IEmailSender>
{
    protected override void BuildOptions(IFakeOptions<IEmailSender> options)
    {
        options.ConfigureFake(fake =>
        {
            A.CallTo(() => fake.Send(A<Data>.Ignored)).Returns(true);
        });
    }
}

Then if there are certain tests where you want to return false, you could override at that point.