Fix pandas incompatibilities in testing

Author: Kevin D Smith

tox.ini

@@ -97,12 +97,14 @@ commands = {[testenv:conda]commands}
 conda_deps =
     {[testenv]conda_deps}
     pandas==0.22*
+    numpy<=1.20  # pandas is incompatible with newer versions
 
 [testenv:py27-pip]
 commands = {[testenv:pip]commands}
 conda_deps =
     {[testenv]conda_deps}
     pandas==0.22*
+    numpy<=1.20  # pandas is incompatible with newer versions
 
 #
 # Python 3.5
@@ -112,12 +114,14 @@ commands = {[testenv:conda]commands}
 conda_deps =
     {[testenv]conda_deps}
     pandas==0.23*
+    numpy<=1.20  # pandas is incompatible with newer versions
 
 [testenv:py35-pip]
 commands = {[testenv:pip]commands}
 conda_deps =
     {[testenv]conda_deps}
     pandas==0.23*
+    numpy<=1.20  # pandas is incompatible with newer versions
 
 #
 # Python 3.6
@@ -127,12 +131,14 @@ commands = {[testenv:conda]commands}
 conda_deps =
     {[testenv]conda_deps}
     pandas==0.24*
+    numpy<=1.20  # pandas is incompatible with newer versions
 
 [testenv:py36-pip]
 commands = {[testenv:pip]commands}
 conda_deps =
     {[testenv]conda_deps}
     pandas==0.24*
+    numpy<=1.20  # pandas is incompatible with newer versions
 
 #
 # Python 3.7
@@ -142,12 +148,14 @@ commands = {[testenv:conda]commands}
 conda_deps =
     {[testenv]conda_deps}
     pandas==0.25*
+    numpy<=1.20  # pandas is incompatible with newer versions
 
 [testenv:py37-pip]
 commands = {[testenv:pip]commands}
 conda_deps =
     {[testenv]conda_deps}
     pandas==0.25*
+    numpy<=1.20  # pandas is incompatible with newer versions
 
 #
 # Python 3.8