Fix signature of HeadlessGenericDialog#getRadioButtonGroups()

The GenericDialog class returns a Vector here; we should do the same.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Introduce a helper to call methods via reflection in unit tests

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Use convenience methods in HeadlessCompletenessTest

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Headless: Only override the AWT methods in GenericDialog

Methods such as parseDouble() should *not* be stub'bed out to return 0!
The parseDouble() method -- which is another example of conflating UI code
with non-UI logic -- should be the one from GenericDialog.

Unfortunately, the addition of such methods will make it much more
painful, still, to maintain the headless mode (as if it was not hard
enough already). Hopefully ImageJ 1.x will not introduce more offenders
like that. Knock on head.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Verify that headless mode can call GenericDialog#parseDouble()

Paul van Schayck reported that this stopped working a while ago.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>