Mocking

Mocking is a technique where a dependency to a class is swapped out (mocked) with an alternate/fake equivalent to the functionality so that the class can be tested in isolation from it’s dependencies. For these examples, I’ll be using the mocking framework Moq.

Suppose we have a method that we wanted to mock:

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public interface IPunctuation
{
  string AddExclamationPoint(string s);
}

public class Punctuation : IPunctuation
{
  public string AddExclamationPoint(string s) {
    return s + "!";
  }
}

We use the method like this:

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var punctuation = new Punctuation();
var s = punctuation.AddExclamationPoint("Hello");
// Result: "Hello!"

Mocking this is fairly straighforward using Moq:

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var punctuationMock = new Mock<IPunctuation>();
punctuationMock
  .Setup(p => p.AddExclamationPoint(It.IsAny<string>()))
  .Returns("HardcodedResult");
var punctuation = punctuationMock.Object;

Once mocked, we use it in the exact same way as we use the real Punctuation class, but with the mocked result:

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var s = punctuation.AddExclamationPoint("Hello");
// Result: "HardcodedResult"

That’s mocking. For more on mocking, see Moq’s documentation.

Extension Methods

Extension methods in C# are static methods that provide some helpful syntax to make code that consumes them a little more readable (and chainable).

We can change the method above to an extension method by making the class and method static and by adding the this keyword:

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public static class PunctuationExtensions
{
  public static string AddExclamationPoint(this string s) {
    return s + "!";
  }
}

And the usage of the extension method is a little cleaner:

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var s = "Hello".AddExclamationPoint();
// Result: "Hello!";

Mocking Extension Methods

I love to mock things when testing, and I love using extension methods, because I find both to be very helpful in writing clean, maintainable code. But how can we mock an extension method?

In the example above, how would I mock out the AddExclamationPoint() method from the PunctuationExtensions class?

Well, you can’t.

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When working in development, sometimes you need to use an SSL certificate. There is no need to pay a provider to sign one for you, because you can create a ‘self signed’ certificate. IIS can do this out of the box for localhost - for more Information, see Scott Guthrie’s walkthrough on creating a self signed certificate in IIS.

That worked great, for a while. But with Chrome 58, which was released in May 2017, a new security feature was introduced which prevents Chrome from trusting a self-signed certificate generated by IIS. The problem is that IIS generates a self signed SSL certificate that doesn’t include a SubjectAlternativeName (SAN), and starting with Chrome 58, certificates without a SAN are seen as insecure.

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