Frequently when integration testing an application, it is desirable to re-configure some parts of it (i.e., special symbol defaults, new service overrides, special service configurations), which currently is ad-hoc or otherwise awkward.
How about if there was a special JVM system property: tapestry.execution-mode. This would be a comma-seperated list of mode names. For each one, the T5 filter would check for a <init-parameter> named "tapestry.foo-modules" (where "foo" is a mode name) and add those to the Registry. The default value for execution-mode would be "production" ... thus you could easily have certain module classes loaded for normal production and a different set loaded for integration testing.