I was trying to reload some variables today for rcov.el, since the rcov.el file uses old syntax for the rake commmand, it uses "rake rcov" instead of "rake test:test:rcov".
So, I copied those lines into my *scratch* buffer, and tried to evaluate them with C-j.
(defvar rcov-command-line "rake test:test:rcov RCOVOPTS='--gcc --no-html'"
"Rcov command line to find uncovered code.
It is good to use rcov with Rake because it `cd's appropriate directory.
`--gcc' option is strongly recommended because `rcov' uses compilation-mode.")
It didn't work because defvar only sets variables if they're not already set, plus, it uses a docstring. What I needed instead was good old setq:
(setq rcov-command-line "rake test:test:rcov RCOVOPTS='--gcc --no-html'")