Background

The test/test_nn.py file is a huge monolith that is too large to work with comfortably; it doesn't load fully in GitHub, syntax highlighting breaks in vim, etc. We should break it up to be more manageable.

Proposal

There's a few different ways to go about this:

1. Split the existing test classes (e.g. TestNN, TestNNDeviceType, etc.) into separate files.
   • Easiest, most direct way to split test_nn.py into smaller files.
   • There are currently 11 different test classes, some of which have very few tests (looking at you, TestFunctionalPickle).
   • Probably not the best long-term, since it doesn't keep related tests together. For example, it's common to add tests to both TestNN and TestNNDeviceType for a new module.
2. Split tests by module type, mirroring the structure in torch/nn/modules.
   • For example, pooling-related tests would go in test/nn/pooling.py.
   • Each would need a separate test class for device-agnostic and device-specific tests.
   • Might need some way to maintain / enforce the mirroring, although changes in torch/nn/modules don't happen too often.
   • There are lots of tests in test_nn.py that aren't module specific that still need a home.
3. ???

Note: At any given point, there are generally several outstanding PRs touching test_nn.py. So actually accomplishing the splitting, whichever way it goes, will be lots of fun :)

cc @albanD @mruberry @jbschlosser