Add missing pytest 5 tests

Author: dmtucker

tox.ini

@@ -4,6 +4,7 @@ min_version = 3.7.0
 isolated_build = true
 envlist =
     py{34, 35, 36, 37}-pytest{2.8, 2.x, 3.0, 3.x, 4.0, 4.x}-mypy{0.57, 0.5x, 0.60, 0.6x}
+    py{35, 36, 37}-pytest{5.0, 5.x}-mypy{0.57, 0.5x, 0.60, 0.6x}
     py{35, 36, 37}-pytest{2.8, 2.x, 3.0, 3.x, 4.0, 4.x, 5.0, 5.x}-mypy{0.70}
     py{35, 36, 37, 38}-pytest{2.8, 2.x, 3.0, 3.x, 4.0, 4.x, 5.0, 5.x}-mypy{0.71, 0.72, 0.73, 0.74, 0.7x}
     flake8