<B>NoteB>: while test_app is a method, it is by default exported as a
subroutine into the namespace that uses App::Cmd::Tester. In other words: you
probably dont need to think about this as a method unless you want to subclass
my $result = test_app($app_class => \@argv_contents);
This will locally set @ARGV to simulate command line arguments, and will
then call the run method on the given application class (or application).
Output to the standard output and standard error filehandles will be captured.
$result is an App::Cmd::Tester::Result object, which has methods to access
the following data:
stdout - the output sent to stdout
stderr - the output sent to stderr
output - the combined output of stdout and stderr
error - the exception thrown by running the application, or undef
run_rv - the return value of the run method (generally irrelevant)
exit_code - the numeric exit code that wouldve been issued (0 is okay)