Component Testing C: How to test a static variable of a function

Answer

Modify your code under test, if you really need access to this variable. The reason is that you can not test from within the test script.

If modifying the code under test is not an option, you need to plan your test script more carefully. You might need several test scripts or test executions, because you can not reset this variable.

Example

For example, the code under test contains the following function.

can you test the variable invisible?

Workaround
The only possibility is to make the variable visible outside the function during testing.
If you can change the code under test, you can introduce a macro, for example _TESTRT_TEST. When you define _TESTRT_TEST, the variable is visible to the test script. You need to define this macro when you generate the test script as well as during the compilation of the code under test.

You can use the macro as follows: 

1. In the Settings dialog box put _TESTRT_TEST in the section:
   Build > Compiler > Preprocessor macro definitions.
2. Declare the variable in the test script, .ptu, as a global variable global. For example:

Why is it impossible to test the variable without modifying the code under test?

Outside of Test RealTime, how would you test this variable? How would you modify it from another function?

The C language does not allow you to access a static variable outside of the function in which the variable is declared. That is the whole point of making the variable static to the function in the first place.

Therefore, if you do not modify your code under test, you need to find a sequence of tests. With this sequence you can pass by all possible states of this static variable. You modify the external interfaces to the function, its parameters and the global variables that it uses.

Which sequence to choose depends upon the code in the function under test. Therefore the answer is outside the scope of this technote.