20.4. Running Tests in Visual Studio

In the previous section, we built [EmptyTest] in our CarTests class. Now, we are ready to run this test. We will walk you through one way to run tests using the built in test runners in VS.

20.4.1. Mac Users: Running Tests

For Mac users, run the CarTests project just like you would any other project.

Note

If the panel does not open once the tests are finished running, look for the Test Results panel name on the margins of your IDE and open it manually.

If you can’t find it, search for “Test” in the VS search bar.

20.4.2. Windows Users: Running Tests

For Windows users, you’ll want to find and open the Test Explorer panel. If you don’t already have it docked, you can find it listed in the top Test menu.

WINDOWS: Visual Studio open Test Explorer

With the panel open, select the Run All Tests option.

Note

If you see that the test fails to run, either passing or failing, you may need to adjust a setting to use 64bit processing.

WINDOWS: Set Test Explorer to use x64 process

You may also need to update some of the testing packages. Right click on the CarTests project and select Manage NuGet Packages…. If you see some items in the Update section of the panel that opens, run the updates. Close and reopen the Team Explorer panel and Visual Studio to ensure the changes are applied.

20.4.3. All Users: Output

Once you run the test, you will see a new output panel with a green check mark indicating the test passed and a message stating the test passed.

20.4.4. Creating Tests

We now know how the test runner behaves when a test passes and can begin the real work of unit testing the Car class. One responsibility of the Car class constructor is to set its initial gasTankLevel field. This field is determined by the constructor argument for gasTankSize .

Car.cs:

// Gas tank level defaults to a full tank
GasTankLevel = gasTankSize;

This class-specific behavior is a good item to test. Under your second TODO, write a test to verify that the constructor sets the gasTankLevel field.

Note

To test the Car class, we must make it available to us by adding using CarNS; to the top of your file. CarNS is the namespace we have assigned to the Car class. Namespaces are used in C# to organize code. You’ve seen them before in other using statements.

//TODO: constructor sets gasTankLevel properly
[TestMethod]
public void TestInitialGasTank()
{
   Car test_car = new Car("Toyota", "Prius", 10, 50);
   Assert.AreEqual(10, test_car.GasTankLevel, .001);
}

Here, we give the test a descriptive name, TestInitialGasTank(), initialize a new Car object, and test that the constructor correctly sets the gasTankLevel field.

We’ve done our best to address Testing Best Practices:

1. The AAAs

   1. We arrange the one variable our test requires: test_car.

   2. We act on the Car constructor method as well: new Car("Toyota", "Prius", 10, 50);.

   3. We assert that the expected value of 10 will equal the actual value returned from getting the tank level (test_car.GasTankLevel).

2. Deterministic

   As it is written, we expect that our test will always pass.

3. Relevant

   This is our first real test, so we don’t yet have much to group it with. That said, the test assesses a method in Car and is situated in a class called CarTests, so it meets the minimum requirements or relevancy. The next section gives us another attribute to use to help group testing variables.

4. Meaningful

   Our test evaluates a simple field assignment but it is not trivial. The line in the constructor being tested is not very complex, but this makes for a good unit test. We want to make sure the basic functionality of our class works as we expect.

Run CarTest to see that both tests pass.

Tip

If you want to rerun only one test, right click on its listing in the results pane.