chore: improve test coverage

[mhamilton723]

[mhamilton723]

/azp run

[azure-pipelines[bot]]

Azure Pipelines successfully started running 1 pipeline(s).

[codecov[bot]]

Codecov Report

Merging #1104 (e1356f6) into master (84f96e9) will increase coverage by 0.23%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1104      +/-   ##
==========================================
+ Coverage   85.77%   86.01%   +0.23%     
==========================================
  Files         250      250              
  Lines       11480    11462      -18     
  Branches      598      598              
==========================================
+ Hits         9847     9859      +12     
+ Misses       1633     1603      -30     

Impacted Files	Coverage Δ
core/src/main/python/mmlspark/core/schema/Utils.py	90.90% <ø> (+30.12%)	:arrow_up:
.../execution/streaming/continuous/HTTPSourceV2.scala	92.08% <0.00%> (-0.72%)	:arrow_down:
.../apache/spark/ml/feature/FastVectorAssembler.scala	60.27% <0.00%> (+15.06%)	:arrow_up:
...ala/org/apache/spark/ml/param/DataFrameParam.scala	83.33% <0.00%> (+16.66%)	:arrow_up:

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