Add Tests for getStep function

[tech4GT]

Add the following tests for the API function getStep which gets the previous steps

• Test for the the blend module

• once we have meta modules, we could pass in a module which has a callback build into its draw method, and confirm that the callback gets called with a correct value for some getStep() output.

• Remove these lines

  image-sequencer/src/modules/Invert/Module.js

  Lines 15 to 17 in 09c4f25

  	console.log(getStep(-2).options.name);
  	console.log(getStep(-1).options.name);
  	console.log(getStep(0).options.name);

[jywarren]

GitMate.io thinks the contributor most likely able to help you is @jywarren.

Possibly related issues are #51 (More Testing), #230 (Add test coverage monitoring via CodeClimate), #27 (add fisheyegl module), #157 (Add a Contrast module), and #113 (Add a Brightness module).