Describing assertions and the assertor
  - An Assertor makes an Assertion.
 
  - An Assertor may be a Person or a Tool.
 
  - An Assertion is a statement about how a TestSubject performs on a
    TestCase.
 
  - This statement is the TestResult.
 
  - An Assertor can make Assertions for a particular Platform and/or a
    particular version of a tool.
 
  - An Assertor's Assertion is made on a certain Date. It can apply to a
    snapshot of the TestSubject.