open stepper, make sure it works for (+ 3 4).

make sure that stepper button appears and disappears as necessary when
language level changes.

Make sure that you get a warning when you change the underlying program, and a
warning when the program window disappears.

Try stepping backward and forward through programs with correct and erroneous
(syntax errors, runtime errors) executions, incl. jumping to end.

Try programs which print snips (print-convert-test.ss)

try programs that contain test cases; make sure that the popups behave sensibly.

