[tests] Speed up test_chunkteacher

[stephenroller]

Patch description
Speed up some slower basic unit tests, mostly by removing a combinatorial explosion of options that isn't really necessary. These tests are also somewhat flaky but hopefully this also helps with that.

Testing steps
Before:

29.17s call     tests/test_chunkteacher.py::TestNumExamples::test_slow_batchsort
26.23s call     tests/test_chunkteacher.py::TestNumExamples::test_slow_dynb
25.44s call     tests/test_chunkteacher.py::TestNumExamples::test_mp_slow_batchsort
22.49s call     tests/test_chunkteacher.py::TestBackgroundPreprocessorNumExamples::test_mp_slow_dynb
22.28s call     tests/test_chunkteacher.py::TestBackgroundPreprocessorNumExamples::test_mp_slow_batchsort
18.69s call     tests/test_chunkteacher.py::TestBackgroundPreprocessorNumExamples::test_slow_dynb
18.63s call     tests/test_chunkteacher.py::TestBackgroundPreprocessorNumExamples::test_slow_batchsort
12.64s call     tests/test_chunkteacher.py::TestNumExamples::test_slow_bs3
12.55s call     tests/test_chunkteacher.py::TestNumExamples::test_slow_bs2
12.53s call     tests/test_chunkteacher.py::TestNumExamples::test_slow_bs1
======= 60 passed, 113 warnings in 477.21s (0:07:57) =======

After:

$ pytest tests/test_chunkteacher.py
15.95s call     tests/test_chunkteacher.py::TestSlowChunk::test_slow_dynb
10.15s call     tests/test_chunkteacher.py::TestSmallBuffer::test_mp_small_buffer_batchsort
9.12s call     tests/test_chunkteacher.py::TestNumExamples::test_mp_normal_dynb
8.19s call     tests/test_chunkteacher.py::TestNumExamples::test_normal_dynb
8.04s call     tests/test_chunkteacher.py::TestBackgroundPreprocessorNumExamples::test_mp_normal_dynb
7.80s call     tests/test_chunkteacher.py::TestSmallBuffer::test_mp_small_buffer_dynb
5.24s call     tests/test_chunkteacher.py::TestNumExamples::test_mp_normal_bs3
5.10s call     tests/test_chunkteacher.py::TestNumExamples::test_normal_batchsort
4.96s call     tests/test_chunkteacher.py::TestBackgroundPreprocessorNumExamples::test_mp_normal_bs3
4.77s call     tests/test_chunkteacher.py::TestSmallBuffer::test_mp_small_buffer_bs3
======= 22 passed, 113 warnings in 104.89s (0:01:44) =======

[jxmsML]

why is this removed?

[stephenroller]

I believe it's redundant with the others. We have a non-multprocessing batchsize 1, and we have multiprocessing with other batchsizes. The explicit combination seems unnecessary.

Same goes for some of the other things I filtered out. I decided to test some things in isolation, rather than the combinatorial explosion of options.

[jxmsML]

do you think the remaining test would catch sth like distributed_world_size > 1 while batchsize = 1 (is this sth that is necessary to test?)

[stephenroller]

No, I don't think they will. I can bring that one back if you'd like.

[jxmsML]

LGTM!! Thanks for the fix! 🚀