Fixed multi validation and wrong fail calls in unit tests

* Positive test was calling the same check several times. Replaced
  with one call.
* Negative test was failing with "'object has no attribute 'assertFail'"
  error message in case of failure. Replaced with appropriate message.

Change-Id: Id03a452f7735d6b4d13f54036f1bd3ae50cb487a
Merge "Fixed multi validation and wrong fail calls in unit tests"