Don't use deprecated add_parameters in tests

[jenshnielsen]

#1334 deprecated DataSet.add_parameters but some tests were still using it. IMHO we should either

• Not use deprecated methods in tests
• If we have tests that explicitly test the deprecated methods they should stay until the method is removed but the warnings should be filtered

In this case the tests does not seem to be testing add_paramters specifically so I just changed them to use add_parameter

[WilliamHPNielsen]

I like it. @astafan8, do you have anything against doing it this way?

[codecov]

Codecov Report

Merging #1343 into master will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1343      +/-   ##
==========================================
- Coverage   72.86%   72.84%   -0.03%     
==========================================
  Files          74       74              
  Lines        8588     8588              
==========================================
- Hits         6258     6256       -2     
- Misses       2330     2332       +2

[astafan8]

This is lovely! no objections :)