You can do the following:

• Just define a goto label just before the test you want to run
• Add option handling to your test script, e.g.

  use Getopt::Long;
  GetOptions("fast" => \$do_fast_test) or die;
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• After test initialization code, add

  goto FAST_TEST_LABEL if $do_fast_test
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• And call the test with perl -Mblib t/testfile.t -fast

If you have planned the number of tests, then you will get an error that too less tests were run (of course), but you can just ignore this or use no_plan.