Update tests to support conversion of NaN as NULL in pyarrow 0.14.*. (#8785)

* Treat NaN as NULL when converting from pandas to arrow.

Fixes broken unit tests from latest pyarrow release.

* Remove outdated pyarrow comment.

Author: tswast

bigquery/noxfile.py

@@ -38,7 +38,6 @@ def default(session):
     for local_dep in LOCAL_DEPS:
         session.install("-e", local_dep)
 
-    # Pyarrow does not support Python 3.7
     dev_install = ".[all]"
     session.install("-e", dev_install)
 

bigquery/tests/unit/test__pandas_helpers.py

@@ -488,7 +488,10 @@ def test_bq_to_arrow_array_w_special_floats(module_under_test):
     roundtrip = arrow_array.to_pylist()
     assert len(rows) == len(roundtrip)
     assert roundtrip[0] == float("-inf")
-    assert roundtrip[1] != roundtrip[1]  # NaN doesn't equal itself.
+    # Since we are converting from pandas, NaN is treated as NULL in pyarrow
+    # due to pandas conventions.
+    # https://arrow.apache.org/docs/python/data.html#none-values-and-nan-handling
+    assert roundtrip[1] is None
     assert roundtrip[2] == float("inf")
     assert roundtrip[3] is None