cd recognizes - argument

'cd -' returns to the previous directory.

This is not valid if no directory change has happened before.
Test for cd -

(minor fixup by sitaram)
Add directive and reason for plan, ok, fail

TAP supports two directives: SKIP and TODO
Both directives also support a reason.

These directives can be supplied to plan, ok, and not ok.

http://testanything.org/tap-specification.html