These tests were caught in the crossfire of the transition to testify.
testify has a few subtle differences from the similar custom framework
it replaced:
- Error behaves differently
- Equal takes its arguments in a different order
This PR also takes the opportunity to use a few shorthands from testify,
such as Len, True, and False.
Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>