tests: make pytest-xdist optional

Author: blueyed

.travis.yml

@@ -6,7 +6,7 @@ jobs:
   include:
     - stage: baseline
       python: 3.6
-      env: TOXENV=py36-dj20-postgres-coverage
+      env: TOXENV=py36-dj20-postgres-xdist-coverage
       services:
         - postgresql
     - python: 3.6

setup.py

@@ -42,7 +42,6 @@ def read(fname):
         'testing': [
             'Django',
             'django-configurations>=2.0',
-            'pytest-xdist>=1.15',
             'six',
         ],
     },

tox.ini

@@ -26,6 +26,7 @@ deps =
     coverage: coverage-enable-subprocess
 
     pytest41: pytest>=4.1,<4.2
+    xdist: pytest-xdist>=1.15
 
 setenv =
     PYTHONPATH = {toxinidir}:{env:PYTHONPATH:}