Work around codecov.io connection failures

tests/coverage/upload_codecov.py

@@ -0,0 +1,16 @@
+#!/bin/env/python
+
+from subprocess import call
+import time
+
+if __name__ == '__main__':
+    max_tries = 10
+    num_tries = 1
+    cmd = 'codecov --required'
+    rc = call(cmd)
+    while rc != 0 and num_tries < max_tries:
+        time.sleep(5)
+        rc = call(cmd)
+        num_tries += 1
+
+    raise SystemExit(rc)

tox.ini

@@ -71,7 +71,7 @@ basepython = python3.8
 commands =
     python -m coverage run test.py -u
     coverage report -m
-    codecov
+    - python tests/coverage/upload_codecov.py  # do not report error if codecov upload fails
 
 # Envs that will test installation from a wheel
 [testenv:wheelinstall-py35]