[BUG] cuDF Pandas now requires pytest at runtime

[beckernick]

It looks like we currently have an explicit runtime dependency on pytest (via assert_eq) in 24.08, blocking cuDF Pandas in the default RAPIDS/cuDF runtime environment (since it doesn't include pytest). Looks like it may have been introduced in this PR.

We should gate this functionality behind a conditional import or find an alternative approach.

In [2]: %load_ext cudf.pandas
---------------------------------------------------------------------------
ModuleNotFoundError                       Traceback (most recent call last)
Cell In[2], line 1
----> 1 get_ipython().run_line_magic('load_ext', 'cudf.pandas')

File /raid/nicholasb/miniconda3/envs/rapids-24.08/lib/python3.10/site-packages/IPython/core/interactiveshell.py:2480, in InteractiveShell.run_line_magic(self, magic_name, line, _stack_depth)
   2478     kwargs['local_ns'] = self.get_local_scope(stack_depth)
   2479 with self.builtin_trap:
-> 2480     result = fn(*args, **kwargs)
   2482 # The code below prevents the output from being displayed
   2483 # when using magics with decorator @output_can_be_silenced
   2484 # when the last Python token in the expression is a ';'.
   2485 if getattr(fn, magic.MAGIC_OUTPUT_CAN_BE_SILENCED, False):

File /raid/nicholasb/miniconda3/envs/rapids-24.08/lib/python3.10/site-packages/IPython/core/magics/extension.py:33, in ExtensionMagics.load_ext(self, module_str)
     31 if not module_str:
     32     raise UsageError('Missing module name.')
---> 33 res = self.shell.extension_manager.load_extension(module_str)
     35 if res == 'already loaded':
     36     print("The %s extension is already loaded. To reload it, use:" % module_str)

File /raid/nicholasb/miniconda3/envs/rapids-24.08/lib/python3.10/site-packages/IPython/core/extensions.py:62, in ExtensionManager.load_extension(self, module_str)
     55 """Load an IPython extension by its module name.
     56
     57 Returns the string "already loaded" if the extension is already loaded,
     58 "no load function" if the module doesn't have a load_ipython_extension
     59 function, or None if it succeeded.
     60 """
     61 try:
---> 62     return self._load_extension(module_str)
     63 except ModuleNotFoundError:
     64     if module_str in BUILTINS_EXTS:

File /raid/nicholasb/miniconda3/envs/rapids-24.08/lib/python3.10/site-packages/IPython/core/extensions.py:77, in ExtensionManager._load_extension(self, module_str)
     75 with self.shell.builtin_trap:
     76     if module_str not in sys.modules:
---> 77         mod = import_module(module_str)
     78     mod = sys.modules[module_str]
     79     if self._call_load_ipython_extension(mod):

File /raid/nicholasb/miniconda3/envs/rapids-24.08/lib/python3.10/importlib/__init__.py:126, in import_module(name, package)
    124             break
    125         level += 1
--> 126 return _bootstrap._gcd_import(name[level:], package, level)

File <frozen importlib._bootstrap>:1050, in _gcd_import(name, package, level)

File <frozen importlib._bootstrap>:1027, in _find_and_load(name, import_)

File <frozen importlib._bootstrap>:1006, in _find_and_load_unlocked(name, import_)

File <frozen importlib._bootstrap>:688, in _load_unlocked(spec)

File <frozen importlib._bootstrap_external>:883, in exec_module(self, module)

File <frozen importlib._bootstrap>:241, in _call_with_frames_removed(f, *args, **kwds)

File /raid/nicholasb/miniconda3/envs/rapids-24.08/lib/python3.10/site-packages/cudf/pandas/__init__.py:10
      6 import warnings
      8 import rmm.mr
---> 10 from .fast_slow_proxy import is_proxy_object
     11 from .magics import load_ipython_extension
     12 from .profiler import Profiler

File /raid/nicholasb/miniconda3/envs/rapids-24.08/lib/python3.10/site-packages/cudf/pandas/fast_slow_proxy.py:20
     17 import numpy as np
     19 from ..options import _env_get_bool
---> 20 from ..testing._utils import assert_eq
     21 from .annotation import nvtx
     24 def call_operator(fn, args, kwargs):

File /raid/nicholasb/miniconda3/envs/rapids-24.08/lib/python3.10/site-packages/cudf/testing/_utils.py:13
     11 import numpy as np
     12 import pandas as pd
---> 13 import pytest
     14 from numba.core.typing import signature as nb_signature
     15 from numba.core.typing.templates import AbstractTemplate

ModuleNotFoundError: No module named 'pytest'

[wence-]

Yes, we should gate.