Using Load in a test methods makes the test pass

The following test Passed! Why is that?

classdef minExample < matlab.unittest.TestCase
 
    properties
       
    end
 
    methods(Test)
 
        function test1(testCase)
            % comment
            save matlab
            load matlab
            verifyEqual(testCase,1,2);
        end
         
    end
 
end

[Erik van Oene]

Run it using:

test = minExample
test.run

the outcome I get is:

ans = 
  TestResult with properties:
          Name: 'minExample/test1'
        Passed: 1
        Failed: 0
    Incomplete: 0
      Duration: 0.1692
Totals:
   1 Passed, 0 Failed, 0 Incomplete.
   0.1692 seconds testing time.

Answer 1

[Andy Campbell]

Hi Erik,

The problem here is indeed the fact that the testCase is getting overwritten. Hence why if you assign the output of the load command to a structure the issue is not encountered. These steps are similar to something like the following:

classdef SomethingNotATestCase
    methods
        function verifyEqual(obj,varargin)
            % do something else
        end
    end
end

Then inside the test, doing something like this:

classdef minExample < matlab.unittest.TestCase
 
    methods(Test)
 
        function test1(testCase)
            testCase = SomethingNotATestCase
            verifyEqual(testCase,1,2);
        end
         
    end
 
end

In both of these cases you have overwritten the testCase with something that is not the right thing to produce a test failure. This is perfectly allowable by the language. This is part of the reason why it is suggested to use the functional form of the load command, including with the output argument, because when you dont use the output argument you "poof" variables into the workspace, and this can overwrite existing variables. If you assign it to an output argument then you explicitly name your variable, and are much less likely to overwrite another variable unknowingly.

Hope that helps!

Andy

Answer 2

[per isakson]

Looks like a bug to me, however in programs one ought to use the functional form

S = load('matlab.mat');

In that case the test fails as expected.

[Erik van Oene]

That is true, though, I don't want the variable of my 'old' workspace (saved in matlab.mat) to be loaded as a structure 'S'. So I changed the line you suggested to:

load('matlab.mat')\

which again makes this test Pass.

Problem is probably that 'testCase' is destroyed/overwritten when saving and loading it. Thought, if this is the reason, I expect any failure or error other than letting a test pass which clearly should not.

Erik

[per isakson]

My memory fails me. However, when the current Matlab oop-stuff was introduced 10+ years ago there was a great deal of discussion about saving and loading objects.

Have a look at Save and Load Process for Objects

[per isakson]

Maybe this is of interest to you General-use object copy

Did you contact the Mathworks' tech-support?