Migrated test towards unit-style.

This test was intended to check the internal behavior of a type and thus is more of a unit test. In this spirit, we've migrated more towards this style by stubbing an internal variable to observe the type's behavior.
Removed unnecessary exports.
Merge pull request #965 from katco-/lp-1272407-prov-test-flaky

Migrated test towards unit-style.

https://bugs.launchpad.net/juju-core/+bug/1272407

This test was intended to check the internal behavior of a type and thus is more of a unit test. In this spirit, we've migrated more towards this style by stubbing an internal variable to observe the type's behavior.