Add tests for Probe.runProbe() method
Add tests for Probe.runProbe() method

By using fakeTime{}, a timeT implementation that returns a static
time.Time for Now(), and testProber{}, a Probe implementation that
returns a static Result when Probe() is called, we can specify the
original state of the Probe, and the expected subsequent state after
probing (triggered by a Probe() run, normally).

hkjn/prober