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I am trying to learn unit testing. I am trying to unit test some Memembership stuff I am making in asp.net mvc 1.0. I been following a book on MVC and I am confused about some stuff that hopefully someone can clear up for me. I am using Nunit and Moq for my frameworks. Question 1: ``` public AuthenticationController(IFormsAuthentication formsAuth, MembershipProvider provider) { FormsAuth = formsAuth ?? new FormsAuthenticationWrapper(); Provider = provider ?? Membership.Provider; } ``` I am kinda confused what "??" does I never really seen it before. Like I don't even know whats happening really in here. Like they passin the interface and then "??" mark happens and makes a new FormsAuthenticationWraper is made? Question 2. ``` public AuthenticationController(): this(null, null) { } ``` I know this is the default constructor but I am not sure why ": this(null,null)" is doing. Like what is it implementing? and what is this refering too. And on top of it why can't that be just left out? A…

Accepted Answer

Question 1

The `??` is called the null-coalescing operator, and is a very useful feature of C# 2.0 onwards.

In your case,

```
FormsAuth = formsAuth ?? new FormsAuthenticationWrapper();
```

simply means "assign `formsAuth` to `FormsAuth` unless it is null, in which case assign `new FormsAuthenticationWrapper()`". It's basically a way of preventing null references in your code. You can also think of it as a shortcut for the following conditional expression:

```
FormsAuth = formsAuth != null ? formsAuth : new FormsAuthenticationWrapper();
```

Question 2

The use of `this(null, null)` is called constructor chaining. All this means is that that the constructor in the same class (hence `this`, as opposed to `base` for the parent class) that takes two parameters, should be called before the body of the constructor is executed.

Overloading constructors is a common practice to make it easier for the developer to create new objects when they just want to use the default properties/settings.

Question 3

As others have mentioned, this really belongs as a separate question. Unlike the previous two, it's much more specific to the context/your code, rather than language features of C#.

Update

Ok, what I've done now is actually rewritten the two constructors here, since I think putting them in another (virtually equivalent) form might be a bit clearer, and is probably better design practice too. The null coalescing operator isn't necessary here.

```
public AuthenticationController()
    : this(new FormsAuthenticationWrapper(), Membership.Provider)
{
}

public AuthenticationController(IFormsAuthentication formsAuth,
    MembershipProvider provider)
{
    this.FormsAuth = formsAuth;
    this.Provider = provider;
}
```

In this form, it should be obvious that the constructor that takes two parameters simply assigns the class variables to the values of the arguments. The parameterless constructor (often called the default constructor) simply creates a new object using the default `FormsAuth` and `Provider` objects, which are specified via constructor chaining.

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