Rule Development
We generally do this through Bugzilla; a rule that looks good is taken by the dev team and checked into the SVN rules file rules/70_testing.cf
, whereby a distributed group of contributors will test it against their corpus in the nightly mass-check run. The resulting collated accuracy data can be viewed at [http://www.pathname.com/~corpus/ this site].
This is changing, however... the current plan is to use RuleSandboxes.
MassesOverview describes a number of tools that are useful in evaluting the quality of prospective rules.
CustomRulesets illustrates rules available from third parties and has links to their mass-check results.