Fix matrix implementation in unit tests

[geofjamg]

Signed-off-by: Geoffroy Jamgotchian [email protected]

Please check if the PR fulfills these requirements (please use '[x]' to check the checkboxes, or submit the PR and then click the checkboxes)

• The commit message follows our guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

Does this PR already have an issue describing the problem ? If so, link to this issue using '#XXX' and skip the rest
No

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
Bug fix

What is the current behavior? (You can also link to an open issue here)
Sparse implementation is used by a few tests.

What is the new behavior (if this is a feature change)?
Dense implementation is used in all unit tests.

Does this PR introduce a breaking change or deprecate an API? If yes, check the following:

• The Breaking Change or Deprecated label has been added
• The migration guide has been updated in the github wiki (What changes might users need to make in their application due to this PR?)

Other information:

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[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

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100.0% Coverage
0.0% Duplication