The command exist test always returns true regardless of if the command is invalid.

Describe the problem

On Windows, we want to test if a command/cmdlet exists before running it. However, the 'command().exist?‘ test always returns true no matter what command t

Related to icy-arctic-fox/spectator#19 but expanded to support passing a line number within the grouping of a spec. If the line number matches a context block, every spec within that context should be run. The same goes for the describe block. If the line number falls on a specific spec then that should be run specifically, still.