Fix tests to ensure correct post is being checked

Refs #3473
- Change tests to not assume that all inserted fixture data
  will end up with the same millisecond-precision time for
  results sorting.  If a test is set up to check the contents
  of a specific fixture extract it explictly from the results.
Merge pull request #3519 from jaswilli/tests-undefined-key

Fix tests to ensure correct post is being checked