Unittesting Matlab System Block

I want to develop some "Matlab System Blocks". For testing their functionality and debugging their code I would like to Unittest them. The method, that I want to test is the "stepImpl" method of the "Matlab System Block".

Unfortunately the "stepImpl" method is a protected method so I can't Unittest them. I know an alternative is to implement the method in other file as a public method or in the "Matlab System Block" as public Method and use this method in the "stepImpl" Method. I already tried to make the "stepImpl" Method public, but this gave me an error.

However I'm hoping for a better way of Unittesting the "Matlab System Block". Are their any best practises or guidelines?

Answer 1

[Altaïr]

Hey @Tim david,

Since the stepImpl function is protected, creating an inherited subclass and using a class-based unit test can be a good approach. Here is an example using the MySystemBlock system block:

classdef MySystemBlock < matlab.System
    % Example MATLAB System block that doubles the input value
    
    methods (Access = protected)
        function y = stepImpl(obj, x)
            y = 2 * x;
        end
    end
end

The stepImpl method is protected and cannot be tested directly. Therefore, a subclass TestableMySystemBlock can be created:

classdef TestableMySystemBlock < MySystemBlock
    methods (Access = public)
        function y = testStepImpl(obj, x)
            % Directly call the protected stepImpl method
            y = stepImpl(obj, x);
        end
    end
end

A class-based unit test can then be written for this inherited class:

classdef TestMySystemBlockSubclass < matlab.unittest.TestCase
    methods (Test)
        function testStepImpl(testCase)
            % Create an instance of the testable subclass
            sysObj = TestableMySystemBlock;
            
            % Define test cases
            testInputs = [1, 2, 3, 0, -1, -2];
            expectedOutputs = [2, 4, 6, 0, -2, -4];
            
            % Loop through each test case
            for i = 1:length(testInputs)
                % Call the testStepImpl in the inherited class
                actualOutput = sysObj.testStepImpl(testInputs(i));
                
                % Verify the output
                testCase.verifyEqual(actualOutput, expectedOutputs(i), ...
                    'AbsTol', 1e-10, ...
                    sprintf('Failed for input: %d', testInputs(i)));
            end
        end
    end
end

To run the tests, execute the following commands in the MATLAB Command Window:

resultsSubclassMethod = runtests('TestMySystemBlockSubclass');
disp(resultsSubclassMethod);

For more information on writing unit tests, the following command can be executed in the MATLAB Command Window:

web(fullfile(docroot, 'matlab/matlab_prog/ways-to-write-unit-tests.html'))