diff --git a/testing/test_assertrewrite.py b/testing/test_assertrewrite.py
index 02270e157..78a5f2bae 100644
--- a/testing/test_assertrewrite.py
+++ b/testing/test_assertrewrite.py
@@ -66,7 +66,7 @@ class TestAssertionRewrite(object):
         s = """'Doc string'\nother = stuff"""
         m = rewrite(s)
         # Module docstrings in 3.7 are part of Module node, it's not in the body
-        # so we remove it so the following body items have the same indexes on 
+        # so we remove it so the following body items have the same indexes on
         # all Python versions
         if sys.version_info < (3, 7):
             assert isinstance(m.body[0], ast.Expr)
diff --git a/tox.ini b/tox.ini
index 33e5fa02c..e9c1dfa96 100644
--- a/tox.ini
+++ b/tox.ini
@@ -64,8 +64,9 @@ deps =
     mock
     nose
     hypothesis>=3.5.2
+changedir=testing
 commands =
-    pytest -n1 -rfsxX {posargs:testing}
+    pytest -n1 -rfsxX {posargs:.}
 
 [testenv:py36-xdist]
 deps = {[testenv:py27-xdist]deps}
@@ -91,10 +92,11 @@ deps =
     pytest-xdist>=1.13
     hypothesis>=3.5.2
 distribute = true
+changedir=testing
 setenv =
     PYTHONDONTWRITEBYTECODE=1
 commands =
-    pytest -n3 -rfsxX {posargs:testing}
+    pytest -n3 -rfsxX {posargs:.}
 
 [testenv:py27-trial]
 deps = twisted