WIP: add tests that operate at the API level

[bhearsum]

This is inspired by recent frustrations of surprise behaviour by signingscript, and feeling like the current test-every-tiny-little-function-independently tests wouldn't allow for any sort of confident refactoring. These new tests that I'm adding use the same entry point that scriptworker calls into: async_main, and they mock out as little as they possible can. Currently, this is calls to Autograph, and verify_mar_signature, but there will probably be other things mocked out (eg: anything that depends on a signature from a real certificate will need to be mocked).

Running just these new tests alone already achieves 35% coverage overall, and 27% coverage of sign.py:

tests/test_script.py::test_gpg_signing[autograph_gpg] PASSED                                                                                                                                [ 25%]
tests/test_script.py::test_gpg_signing[stage_autograph_gpg] PASSED                                                                                                                          [ 50%]
tests/test_script.py::test_mar_signing[autograph_hash_only_mar384] cPASSED                                                                                                                   [ 75%]
tests/test_script.py::test_mar_signing[stage_autograph_hash_only_mar384] PASSED                                                                                                             [100%]

---------- coverage: platform linux, python 3.11.6-final-0 -----------
Name                              Stmts   Miss Branch BrPart  Cover   Missing
-----------------------------------------------------------------------------
src/signingscript/__init__.py         0      0      0      0   100%
src/signingscript/exceptions.py      11      3      0      0    73%   17, 30, 43
src/signingscript/rcodesign.py       71     58     28      0    13%   25-51, 62-69, 82-90, 99-112, 121-132, 143-152
src/signingscript/script.py          72     29     34      7    55%   32, 34, 37-38, 41-43, 55, 57, 71-74, 112-130, 135-137
src/signingscript/sign.py           863    594    222     14    27%   159-161, 182-184, 202-207, 225-235, 255-269, 294-316, 341-373, 393-407, 430-444, 465-488, 495-500, 508-524, 530-539, 545-562, 568-577, 583-596, 602, 623-630, 637-655, 661-663, 669-687, 693-703, 708-712, 718-721, 727-741, 747-751, 756-763, 769-783, 823-857, 867, 919, 934, 936, 938, 946-948, 952->956, 958-963, 966-969, 975-988, 1014, 1027, 1029, 1054-1063, 1135-1145, 1164-1176, 1192-1200, 1245, 1285-1301, 1324-1332, 1354-1367, 1373-1374, 1393-1468, 1493-1515, 1526-1551, 1558-1559, 1564-1582, 1593-1606, 1611-1619, 1628-1650, 1661-1668, 1677-1681, 1690-1768
src/signingscript/task.py            82     11     36     10    82%   83, 131->130, 134, 157-158, 171, 177, 239, 243, 247, 250, 253
src/signingscript/utils.py           95     33     18      3    59%   63-67, 80-81, 101-104, 132, 143-148, 174-177, 192-203, 229, 243
-----------------------------------------------------------------------------
TOTAL                              1194    728    338     34    35%

This number will obviously go up as I add tests for other signing types.

[ahal]

Overall this stack looks great to me!

[ahal]

Huh, how did I not know that startswith could take a tuple?

[bhearsum]

Neither did I until a few days ago 😆

[bhearsum]

augh, sorry, I just realized this has a whole bunch of stuff from #1085. I'm going to rebase.