CI: troubleshoot openpyxl failures (pandas-dev#30009)

Author: jbrockmendel

ci/deps/travis-36-cov.yaml

@@ -27,7 +27,8 @@ dependencies:
   - numexpr
   - numpy=1.15.*
   - odfpy
-  - openpyxl
+  - openpyxl<=3.0.1
+  # https://github.com/pandas-dev/pandas/pull/30009 openpyxl 3.0.2 broke
   - pandas-gbq
   # https://github.com/pydata/pandas-gbq/issues/271
   - google-cloud-bigquery<=1.11

pandas/tests/io/excel/test_openpyxl.py

@@ -1,8 +1,11 @@
+from distutils.version import LooseVersion
 import os
 
 import numpy as np
 import pytest
 
+from pandas.compat import PY37, is_platform_mac
+
 import pandas as pd
 from pandas import DataFrame
 import pandas.util.testing as tm
@@ -13,6 +16,8 @@
 
 pytestmark = pytest.mark.parametrize("ext", [".xlsx"])
 
+openpyxl_gt301 = LooseVersion(openpyxl.__version__) > LooseVersion("3.0.1")
+
 
 def test_to_excel_styleconverter(ext):
     from openpyxl import styles
@@ -81,6 +86,9 @@ def test_write_cells_merge_styled(ext):
         assert xcell_a2.font == openpyxl_sty_merged
 
 
+@pytest.mark.xfail(
+    openpyxl_gt301 and PY37 and is_platform_mac(), reason="broken change in openpyxl"
+)
 @pytest.mark.parametrize(
     "mode,expected", [("w", ["baz"]), ("a", ["foo", "bar", "baz"])]
 )
@@ -107,7 +115,9 @@ def test_write_append_mode(ext, mode, expected):
             assert wb2.worksheets[index]["A1"].value == cell_value
 
 
-@pytest.mark.xfail(openpyxl.__version__ > "3.0.1", reason="broken change in openpyxl")
+@pytest.mark.xfail(
+    openpyxl_gt301 and PY37 and is_platform_mac(), reason="broken change in openpyxl"
+)
 def test_to_excel_with_openpyxl_engine(ext, tmpdir):
     # GH 29854
     # TODO: Fix this once newer version of openpyxl fixes the bug