[Python] BUG: two failing tests related to ARROW_DEFAULT_MEMORY_POOL in conda builds on unix

[h-vetinari]

Describe the bug, including details regarding any error messages, version, and platform.

#14832 switched on the test suite within the conda-builds, which itself synced with conda-forge/arrow-cpp-feedstock#875

In the process of doing two tests failing with the same error were skipped,

arrow/dev/tasks/conda-recipes/arrow-cpp/meta.yaml

Lines 380 to 381 in 2c768a1

	# "Unsupported backend 'nonexistent' specified in ARROW_DEFAULT_MEMORY_POOL"
	{% set tests_to_skip = tests_to_skip + " or (test_memory and test_env_var)" %} # [unix]

That error looks like:

FAILED test_memory.py::test_env_var - assert 2 == 1
 +  where 2 = len(['WARNING: Logging before InitGoogleLogging() is written to STDERR', "W20221123 12:16:17.825700 443543 memory_pool.cc:113] Unsupported backend 'nonexistent' specified in ARROW_DEFAULT_MEMORY_POOL (supported backends are 'mimalloc', 'jemalloc', 'system')"])

which might indicate a missing default somewhere?

To fix this, the line quoted above should be removed, and the conda tests still pass.

Component(s)

C++, Continuous Integration, Python

[kou]

I think that we should improve our test for -DARROW_USE_GLOG=ON build:

diff --git a/python/pyarrow/tests/test_memory.py b/python/pyarrow/tests/test_memory.py
index 092c50de33..77057bef59 100644
--- a/python/pyarrow/tests/test_memory.py
+++ b/python/pyarrow/tests/test_memory.py
@@ -134,8 +134,14 @@ def check_env_var(name, expected, *, expect_warning=False):
         res.check_returncode()  # fail
     errlines = res.stderr.splitlines()
     if expect_warning:
-        assert len(errlines) == 1
-        assert f"Unsupported backend '{name}'" in errlines[0]
+        assert len(errlines) == 1 or len(errlines) == 2
+        if len(errlines) == 1:
+            # ARROW_USE_GLOG=OFF
+            assert f"Unsupported backend '{name}'" in errlines[0]
+        else
+            # ARROW_USE_GLOG=ON
+            assert f"InitGoogleLoggingd()" in errlines[0]
+            assert f"Unsupported backend '{name}'" in errlines[1]
     else:
         assert len(errlines) == 0