Can I access local functions for unit testing

I want to unit test local functions that appear after the main function of a file, whose name is not the file name. After all it's not really unit testing if I just test the final outcome of the program. Is there any way to call them from a test file? Do I really have to make a new file for every little helper function?

Answer 1

[Jan]

You can call subfunctions only from their main function. This impedes a unit-testing. But the main function can provide a function handle to the subfunction:

subFcnH = YourFcn('giveMeHandles');
subFcnH(0.1) - sin(0.1)  % A simply unit-testing

ans = 0

function out = YourFcn(in)
% If input is a CHAR or string and equals a keyword:
if strcmpi(in, 'giveMeHandles')
    out = @subFcn;
    return;
end

% The actual calculation:
out = subFcn(in);
end

function y = subFcn(x)
y = sin(x);
end

[Jason Klebes]

Thanks. I see, I need to basically add "getters" to the main function which return the local functions from the same file. This is possibly uglier than splitting off each little function into its own file, but possible.

[Steven Lord]

Those local functions are only directly callable by code in that file. If you aren't already "exporting" them as function handles for some other purpose, shouldn't you be testing them through their interface (which would be the main function in the file)?

[Daniel]

Consider a large codebase with many files, each of which contains many local functions. The local functions behavior should be unit testable. Testing only through the main functions interface puts us at least one layer above the functionality under test, making it more difficult to write good tests. This should be obvious, so I won't provide any examples. Now, if in this example tests want to be added, the options to do so are pretty bad - either move all the local functions out into their own files, or modify the main function inputs and outputs (thus requiring modifications to instances throughout the codebase where the main functions are called) to return function handles to all local functions. Both of these options are pretty bad. In node, we could just export the local functions and then test them, without requiring any functional changes to the underlying codebase.

I hope that I am missing something here, but as far as I've been able to tell these are the only options to test local functions, both of which are really unfortunate.

Answer 2

[Mauro DiNuzzo]

I completely understand your frustration, as I've often run into the same limitation and found it quite restricting that MATLAB doesn't allow a straightforward way of calling local functions outside their normal context.

After running into this issue again today, I set out to find a practical workaround for this limitation and ended up creating a small utility that might be exactly what you were looking for. It allows you to "export" local functions from a MATLAB file so that they can be tested independently, without having to restructure your codebase or alter the main function's interface. It’s just a lighweight fix and not a perfect solution (the language imposes some constraints), but for simple and practical use cases, it works as expected.

You can find it here: https://www.mathworks.com/matlabcentral/fileexchange/181583-exports

Hopefully this is still useful to you (even though some time has passed), and I hope it proves helpful for others running into the same issue, at least until Mathworks eventually addresses this and craft a built-in solution.