Update testing.md

[jasalt]

First paragraph had reference to possibly deprecated info.

Second paragraph was definitely out of date looking the current sources. Rewrote it also so it is at least slightly more correct and without typos while some improvement could be made in it's usage with REPL etc.

[jasalt]

On second note, while testing run-tests in REPL session running a test declared in current file ns I found it weirdly stateful, incrementing reported tests passed count every time after running it again during the session.

Not sure if it's a bug or if it's unfinished or something, but haven't faced similar behavior with Clojure.

[Chemaclass]

Nice catch. This was not up-to-date, as this phel function was created mainly to be used on the TestCommand which execute the phel tests: bin/phel test

As you can see, the first argument is definitely a hash-map of options and then the namespaces, your suggestion is correct.