Add tests about generic list of submodels

[GuillaumeDesforges]

I'm struggling with some issues with a generic model with a list of elements of submodels. As I'm trying to solve my own problem, I wrote tests to see if the issue was coming from the library.

Turns out it is not, but I figure it's always useful to add tests.

[codecov-commenter]

Codecov Report

Merging #66 (b49d08c) into dev (2dc6ff1) will increase coverage by 0.04%. The diff coverage is n/a.

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@@            Coverage Diff             @@
##              dev      #66      +/-   ##
==========================================
+ Coverage   93.08%   93.13%   +0.04%     
==========================================
  Files          23       23              
  Lines        1085     1092       +7     
==========================================
+ Hits         1010     1017       +7     
  Misses         75       75              

Flag	Coverage Δ
unittests	93.13% <ø> (+0.04%)	:arrow_up:

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see 3 files with indirect coverage changes

[dapper91]

@GuillaumeDesforges please, change target branch from master to dev

[dapper91]

@GuillaumeDesforges please, change target branch from master to dev

[GuillaumeDesforges]

Sure, sorry about that.