Heracules bravely decapitated the many heads of Hydra!

This change runs headless Firefox instances in parallel. Hydra had lots of heads running in parallel. Heracules made Hydra headless. Forgive me.

Author: davehunt

.travis.yml

@@ -9,7 +9,7 @@ _aliases:
       paths:
         - results
   - &nightly
-    env: FIREFOX=nightly
+    env: FIREFOX=nightly PYTEST_ADDOPTS=-n=auto
     addons:
       <<: *artifacts
       firefox: latest-nightly

requirements/tests.txt

@@ -1,2 +1,3 @@
 pytest==3.3.2
 pytest-selenium==1.11.4
+pytest-xdist==1.22.0

tests/webserver.py

@@ -30,7 +30,7 @@ def translate_path(self, path):
 class WebServer(object):
     """Web server for serving local files within the /web directory."""
 
-    def __init__(self, host='', port=8000):
+    def __init__(self, host='', port=0):
         """Set up web server.
 
         Args:

tox.ini

@@ -3,7 +3,7 @@ envlist = py{27,36}, flake8, docs
 
 [testenv]
 recreate = True
-passenv = DISPLAY MOZ_HEADLESS TRAVIS TRAVIS_JOB_ID TRAVIS_BRANCH
+passenv = DISPLAY MOZ_HEADLESS PYTEST_ADDOPTS TRAVIS TRAVIS_JOB_ID TRAVIS_BRANCH
 deps = -rrequirements/coverage.txt
 commands =
     pytest --driver=Firefox --cov --html=results/{envname}.html {posargs}