Add extra pytest tests

[klaasnicolaas]

Adding extra tests to make sure that users with javascript source and myDeviceArray variable also works fine.

[codecov]

Codecov Report

Merging #22 (4d44857) into master (2c730a0) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master      #22   +/-   ##
=======================================
  Coverage   87.62%   87.62%           
=======================================
  Files           4        4           
  Lines          97       97           
  Branches       12       12           
=======================================
  Hits           85       85           
  Misses          9        9           
  Partials        3        3           

Impacted Files	Coverage Δ
omnikinverter/models.py	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2c730a0...4d44857. Read the comment docs.