tox.ini: add config for isort

Author: blueyed

tox.ini

@@ -205,6 +205,14 @@ filterwarnings =
     # Do not cause SyntaxError for invalid escape sequences in py37.
     default:invalid escape sequence:DeprecationWarning
 pytester_example_dir = testing/example_scripts
+
 [flake8]
 max-line-length = 120
 ignore = E203,W503
+
+[isort]
+; This config mimics what reorder-python-imports does.
+force_single_line = 1
+known_localfolder = pytest,_pytest
+known_third_party = test_source,test_excinfo
+force_alphabetical_sort_within_sections = 1