In a previous post I described how AutoFixture's Do method can let you invoke commands on your SUT with Dummy values for the parameters you don't care about.

The Get method is the equivalent method you can use when the member you are invoking returns a value. In other words: if you want to call a method on your SUT to get a value, but you don't want the hassle of coming up with values you don't care about, you can let the Get method supply those values for you.

In today's example I will demonstrate a unit test that verifies the behavior of a custom ASP.NET MVC ModelBinder. If you don't know anything about ASP.NET MVC it doesn't really matter. The point is that a ModelBinder must implement the IModelBinder interface that defines a single method:

object BindModel(ControllerContext controllerContext,     ModelBindingContext bindingContext);

In many cases we don't care about one or the other of these parameters, but we still need to supply them when unit testing.

The example is a bit more complex than some of my other sample code, but once in a while I like to provide you with slightly more realistic AutoFixture examples. Still, it's only 10 lines of code, but it looks like a lot more because I have wrapped several of the lines so that the code is still readable on small screens.

[TestMethod] public void BindModelWillReturnCorrectResult() {     // Fixture setup     var fixture = new Fixture();     fixture.Customize<ControllerContext>(ob =>         ob.OmitAutoProperties());       var value = fixture.CreateAnonymous("Value");     var bindingContext = new ModelBindingContext();     bindingContext.ValueProvider =         new Dictionary<string, ValueProviderResult>();     bindingContext.ValueProvider["MyValue"] =         new ValueProviderResult(value, value,             CultureInfo.CurrentCulture);       var expectedResult =         new string(value.Reverse().ToArray());     var sut = fixture.CreateAnonymous<MyModelBinder>();     // Exercise system     var result = fixture.Get((ControllerContext cc) =>         sut.BindModel(cc, bindingContext));     // Verify outcome     Assert.AreEqual(expectedResult, result, "BindModel");     // Teardown }

The first part simply creates the Fixture object and customizes it to disable AutoProperties for all ControllerContext instances (otherwise we would have to set up a lot of Test Doubles for such properties as HttpContext, RequestContext etc.).

The next part of the test sets up a ModelBindingContext instance that will be used to exercise the SUT. In this test case, the bindingContext parameter of the BindModel method is important, so I explicitly set that up. On the other hand, I don't care about the controllerContext parameter in this test case, so I ask the Get method to take care of that for me:

var result = fixture.Get((ControllerContext cc) =>     sut.BindModel(cc, bindingContext));

The Get method creates a Dummy value for the ControllerContext, whereas I can still use the outer variable bindingContext to call the BindModel method. The return value of the BindModel method is returned to the result variable by the Get method.

Like the Do methods, the Get methods are generic methods. The one invoked in this example has this signature:

public TResult Get<T, TResult>(Func<T, TResult> function);

There are also overloads that works with the versions of the Func delegate that takes two, three and four parameters.

As the Do methods, the Get methods are convenience methods that let you concentrate on writing the test code you care about while it takes care of all the rest. You could have written a slightly more complex version that didn't use Get but instead used the CreateAnonymous method to create an Anonymous Variable for the ControllerContext, but this way is slightly more succinct.

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Monday, 04 January 2010 20:53:24 UTC


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