Fixed Need to make checks that the callback is a proper function and eventName is a proper value as well #2

Fixed Null/undefined for param values to 'on' and 'once' methods.
Instead of creating 12 objects - create an array `testCases` with properties: eventName, callback, result. Then in the loop check that `events._addListener(testCase.eventName, testCase.callback) equals to testCase.result`