Test impact analysis helps developers to identify which all tests should run after code changes. This feature only available in Ultimate and Premium editions and only works with Managed code.

1. Create a class library project, it is our production code, this library allows numbers to Add and Subtract numbers. And here is the implementation.

   namespace DemoLib
   {
       public class Math
       {
           public int Add(int number1, int number2)
           {
               return number1 + number2;
           }
   
           public int Subtract(int number1, int number2)
           {
               return number1 - number2;
           }
       }
   }
   

2. And here is the Unit Tests for both add and subtract methods.

   using Microsoft.VisualStudio.TestTools.UnitTesting;
   
   namespace DemoLib.Test
   {
       [TestClass]
       public class MathTests
       {
           [TestMethod]
           public void TestAdd()
           {
               int first = 10;
               int second = 20;
               int expected = first + second;
               Math math = new Math();
   
               var actual = math.Add(10, 20);
   
               Assert.AreEqual(expected, actual);
           }
   
           [TestMethod]
           public void TestSubtract()
           {
               int first = 10;
               int second = 20;
               int expected = first - second;
               Math math = new Math();
   
               var actual = math.Subtract(10, 20);
   
               Assert.AreEqual(expected, actual);
           }
       }
   }
   

   And here is TestList View

   

   TestList view

3. We can get the Test Impact view from Test menu, Windows and Select Test Impact View.
   

   Test Impact View

   As it mentioned in the Test Impact View window, we need to enable the Test Impact.

4. To enable Test Impact, edit the Test settings, from Test menu, which will open the Test Settings dialog. Select the Data and Diagnostics option from the left side. And check the Test Impact checkbox from the Grid.
   

   Test settings dialog

5. After enabling Test Impact, using the Test Setting window, select the Test Impact window, now we are ready to track the test impact for that we need to run the unit tests cases.
   

   Test Impact view after enabling Test Impact

6. Now run the unit test cases to enable tracking.
7. Now I am modifying the source code, like the following.

   public int Add(int number1, int number2)
   {
       return System.Math.Abs(number1) + System.Math.Abs(number2);
   }
   

   Instead of adding the numbers directly, now I am adding the positive numbers, by taking absolute values. After changing the code, build the project, , Visual Studio automatically detect all the affected unit test cases and displays it in the Test Impact view. In our case, the TestAdd method.

   

   Test Impact view - Displaying affected unit tests

   It also displays the changed methods. Instead of using the automated way, above mentioned, you can do this manually also. If you are making any code change, right click on the method and you can choose either Show calling Tests or Run calling tests, which will display or run the unit test cases.

   

   Right click on the code, for Show Calling tests or run calling tests

Happy coding