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Using Load in a test methods makes the test pass

Asked by Erik van Oene on 15 Oct 2019
Latest activity Answered by Andy Campbell on 21 Oct 2019 at 12:51
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

  1 Comment

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.

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Products


Release

R2013b

2 Answers

Answer by Andy Campbell on 21 Oct 2019 at 12:51

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

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Answer by per isakson
on 18 Oct 2019

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.

  3 Comments

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
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.
Maybe this is of interest to you General-use object copy
Did you contact the Mathworks' tech-support?

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