Write own unit tests with AxUnit

Goal for this training chapter

After this training session:

you know how a test class looks like
you know how you create a test method within a test class
you know what are assertions and how they're used
use full qualified type identifier for items in namespaces
you know, where you find information for writing test functions
you know where you find guidelines and tips for writing tests

Create a test for the new implemented class valve

Open the file Test_Valve.st in the folder test

Here you can see a template for a test class. It's marked with the pragma {TestFixture}

Tip: You can filter the files in the Explorer:

More information you'll find here

AxUnit support not just test classes. It supports also test functions
Insert a test method. By entering te the snippet test-method will be proposed. And press enter

Test methods will be marked with the pragma {Test}
Change the name of the method to Test_Open_valve_and_Expect_IsOpen_True

Recommendations for writing tests, you'll find here
In the next step we select our class we want to test. Therefore we declare the variable v in the VAR section
```
VAR PRIVATE
    v : Simatic.Ax.Tutorial.Valve;
END_VAR
```
In this case we use the full qualified name for the Valve class. This is an alternative to USING Simatic.Ax.Tutorial;.
To implement the test itself, we modify the method MyTestMethod in this way:
```
{Test}
METHOD PUBLIC Test_Open_valve_and_Expect_IsOpen_True
    v.Open();
    AxUnit.Assert.Equal(actual := v.IsOpen(), expected := TRUE);
END_METHOD
```
Explanation:
1. The method v.Open() calls the method Open of the class valve. In this case we expect, that the method IsOpen() returns the value TRUE
2. The expression Equal(actual := v.IsOpen(), expected := TRUE); contains the assertion Equal which check if the returned value of IsOpen() equals TRUE.
  
  Further assertions are:
  - NotEqual
  - LessThan
  - GreaterThan
  More information regarding testing, you'll find here