Visual Studio 2017 Enterprise provides a feature called Live Unit Testing that enables developers to see live how changing C# and VB.NET code affects its corresponding unit tests. Among its features, it includes showing coverage information in the editor as you type, integration with the Test Explorer, including/excluding targeted test methods or projects for large solutions, quick navigation to failed tests. It works with MSTest, and NUnit, but only for .NET Framework, as support for .NET Standard has not been added yet.

Detailed information about this productivity tool is available in this blog post: Live Unit Testing in Visual Studio 2017 Enterprise. In this article, I will show how this feature help you when you do test driven development. For this purpose, I will create a class called Point3D that is supposed to model a point in 3-dimentional space, as part of a .NET Framework class library called ALibraryHasNoName. A separate unit testing project called ALibraryHasNoName.Test contains an unit testing class Point3DTest. Initially, these are empty.

To start the live unit testing you need to run go to Test > Live Unit Testing and press Start.

I will start by writing a test for the constructor of Point3D. The constructor is supposed to take three arguments, representing the values for the coordinates in the three dimensions, X, Y and Z.

Since the Point3D class is empty, this line of code produces a compiling error. I can use the refactoring tools and create an implementation for the constructor.

After the code is added, when I navigate to the source code document I can see green check marks on the left of the code indicating lines of code covered by successful unit tests.

I don’t like the default names v1, v2, v3 and the fact that these values are represented by fields. I want to use properties called X, Y and Z. Therefore I am refactorying the generated code as shown below:

Back to the unit test, I am adding a few tests for these properties, making sure I get back the values I passed to the constructor.

The result when switching back to the Point3D class is that these properties are now covered by 1 test.

Next thing I want to do is add a static property/field to represent the origin of the 3D space, i.e. the point at (0,0,0). For this I am writing a new test method with the content shown below. Visual Studio suggests several ways to generate the missing symbol: as a property, field or read-only field, which I find the closest to what I want so I am going with this.

The code is generated and I get a visual indication that it is already covered by 1 test.

I want to add tests to make sure the three properties are all 0 as expected.

Back to the source code I can see now that each property is covered by two succesful tests at this point.

If you click the passing indicator, it shows the tests that cover it, whether they passed or failed, and the duration of their execution.

The last thing I want to do for this demo is adding a method to do a translation of the point in the 3d space. I want to call this method Offset. Therefore, I start with a new test method, called TestOffset where I create a point and invoke the new method. Visual Studio suggest to generate the missing method and I will go with the suggested code.

At this point the test is failing. Instead of a green check mark on the left, I see red crosses, indicating a failure.

These marks can be used to get more information about the failure. It turns out that the method is throwing an exception, that is not caught, so the test is failing.

Next, I will change the implementation of the Offset method to reflect what it is expected from it, and the red crosses turn instantly into green check marks.

To check the effect of the function, I am adding tests for each of the three properties of the class.

Going back to the class source code I can see that each of the three properties now has three successful tests that cover them.

Although this post only covers some of the capabilities of live unit testing I hope it shows how helpful it can be in writing unit tests in general and with TDD in particular. For details about the features check the official documentation.

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