Add assertion for Symbol in appropriate tests

[notmessenger]

tests/unit/services/sl-behavior-test.js

• "getBehaviorGroup() requires an Object to be provided"
• "getBehaviorGroup() "provider.behaviorGroup" must be a String or Function"
• "setBehaviors() requires an Object to be provided"
• "isAble() requires two arguments to be provided"
• "isAble() requires first argument to be a String"
• "isAble() requires second argument to be a String or Object"

[notmessenger]

Blocked by #67