Question

My application has the following project structure: There is the Business Logic project and the UnitTesting project where the methods from the Business Logic are tested. No mocking or testing framework are used (we rely on Visual Studio unit tests and we implement our own mock objects).
In the Business Logic let’s say I have the following method:

public static void SomeMethod ()
{
    ....
    if (cond1)
        if (cond2)
           SendMail();
}

I want to unit test that. I don’t want to unit test the sending of the mail, rather the mail is sent under the correct circumstances. So I was thinking to do something like

public class MailSender : ISmtpMail
{
    // stuff
}

public class FakeMailSender : ISmtpMail
{
    //
    static bool SendMail ()
    {
        return true;
    }
}

The problem is that I don’t know how to enforce the usage of the FakeMailSender in the unit test project or in the unit test methods which look something like :

[TestMethod]
public static void SomeMethod_Test()
{
    // some mock initialization
    BusinessLogic.SomeMEthod ();
    // checks
} 

without changing the BusinessLogic method signature or injecting code (which is undesired)

Answer 1

It’s not clear where your first method “lives”. It seems to me that:

• Your SendMail method shouldn’t be static, which makes all kinds of test double injection tricky to say the least
• You should inject ISmtpMail into whatever needs to send mail.

You say you want to do it “without injecting code” – why not? The “mail sending” service is clearly a dependency: your code will be clearer, less tightly coupled, and easier to test if you inject that depedency, whether explictly or with the help of a DI container.