test(number): replace RegExp with validation functions

[xDivisionByZerox]

Description

This PR enhances the type validation in tests for the NumberModule.

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Reasoning

[...] The tests will usually use regex or preferably validator.js to ensure the method returns valid results. [...]

This statement is from the projects CONTRIBUTING.md. The word of interest here is preferably. This is because RexExp can get out of hand really quickly and does not always result in easy-to-understand error messages since they only provide the RegExp and no information on where the error exactly happened.
This problem persist with Validation functions. But, they result in the error message providing the function's name which allows for a quicker evaluation of the actual problem if it is descriptive enough.

[codecov]

Codecov Report

Merging #1857 (5602219) into next (8076bb0) will decrease coverage by 0.01%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             next    #1857      +/-   ##
==========================================
- Coverage   99.63%   99.63%   -0.01%     
==========================================
  Files        2384     2384              
  Lines      238991   238991              
  Branches     1231     1231              
==========================================
- Hits       238125   238122       -3     
- Misses        844      847       +3     
  Partials       22       22              

see 2 files with indirect coverage changes