Right after calling (oos 'load-op :fomus-test),
you should be able to do (fomus-test:run-tests).

If you would like to update the checksums for all
failures, then set fomus-test:*MD5-LEARN-CHECKSUMS*
to T, before calling (fomus-test:run-tests).
To update an individual test e.g. you could invoke:
(5am:run! 'fomus-test::simple-scale.2)
And of course, collections of tests can be called
as well, if they have been declared with (in-suite ...).