Tweak Makefile to so that make test TEST="CMD PIGLE" works

[danielhollas]

With a small tweak to the Makefile, it is now possible to run multiple selected tests, not just one.

To run a single test, one can do:

make test TEST=CMD

Now one can also do (note the quotation)

make test TEST="CMD PIGLE"

(I needed this for #168 )

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.06%. Comparing base (5af1168) to head (4feaa2f).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #218   +/-   ##
=======================================
  Coverage   84.06%   84.06%           
=======================================
  Files          47       47           
  Lines        6614     6614           
  Branches      766      766           
=======================================
  Hits         5560     5560           
  Misses        855      855           
  Partials      199      199           

Flag	Coverage Δ
unittests	18.36% <ø> (ø)

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[JanosJiri]

Nice, this might be quite useful.