With IDLE, I have issues with trying to test IDLE code without retesting tkinter, as well as deciding on the proper units of behavior to test.

Some suggestions: 
1. Add a docstring to the module with guidelines, after review from a couple of others.
For instance,I believe you are saying that no test should explicitly call compile.  Rather the test writer should call compile and extract the bytecode to copy into a test.

2. Make yourself a module code owner so you get informed and can review.  Reviewing would be easier with guidelines to refer to, instead of repeating them.

3. An example issue is that some callables take many types of arguments.  If not already, tests that the function can extract the bytecode from various objects should be separate from tests that extracted bytecode is then handled properly.  Would any internal refactoring of dis and addition of _test functions make it easier to make test more independent of each other?

4. I would rather read the multiple long lists like

expected_opinfo_outer = [
  Instruction(opname='LOAD_CONST', opcode=100, arg=1, argval=3, argrepr='3', offset=0, starts_line=2, is_jump_target=False),
  Instruction(opname='LOAD_CONST', opcode=100, arg=2, argval=4, argrepr='4', offset=3, starts_line=None, is_jump_target=False),
  ...
]

condensed to

expected_opinfo_outer = [Instruction(opname, opcode, arg, argval, argrepr,
                                     offset, starts_line, is_jumps_target)
    for opname, opcode, arg, argval, argrepr, offset, starts_line, is_jumps_target in
(('LOAD_CONST', 100,    1,   3,     '3',      0,      2,           False),
 ('LOAD_CONST', 100,    2,   4,     '4',      3,      None,        False),
 ...
)]