A bit of progress

That issue with IBitmapDrawable...well, I didn't narrow down the exact line that was causing it, but an updated test.hxml file definitely helps (ignoring the cpp target problem, which this doesn't address, hence that target is commented out for now):

## All targets

-main TestMain
-lib munit
-lib hamcrest
-cp C:/HaxeToolkit/haxe/lib/flixel/git
-D flixel=3.3.12
-cp C:/HaxeToolkit/haxe/lib/openfl/3,6,0
-D openfl=3.6.0
-cp C:/HaxeToolkit/haxe/lib/lime/2,9,0
-D lime=2.9.0
-cp C:/HaxeToolkit/haxe/lib/hscript/2,0,5
-D hscript=2.0.5
-cp C:\HaxeToolkit\haxe\lib\openfl/3,6,0/extern
-cp source
-D native-trace
-cp test
-D openfl-next
-D tools=2.9.0
-D flash-use-stage
-D no-compilation
-D openfl-flash
-D fdb
-D web
-D noflxg
-cp export/flash/haxe
--macro flixel.system.macros.FlxDefines.run()
--macro mcover.MCover.coverage([''],['source'])

--each

## Flash 9+

-swf-version 11.8
-swf export/test/coveragetest.swf

#--next

## CPP

#-D HXCPP_M64
#-cpp export/cpp_test

With that, it actually compiles and runs, and the example test passes, with "haxelib run munit t."  Great!  Now, how about an actual test?  To be continued...