Update the pytest dependency to the latest install.

conftest.py

@@ -8,20 +8,8 @@ from parso import cache
 
 collect_ignore = ["setup.py"]
 
-
-def pytest_addoption(parser):
-    parser.addoption("--warning-is-error", action='store_true',
-                     help="Warnings are treated as errors.")
-
-
-def pytest_configure(config):
-    if config.option.warning_is_error:
-        import warnings
-        warnings.simplefilter("error")
-
-
 @pytest.fixture(scope='session')
-def clean_parso_cache(request):
+def clean_parso_cache():
     """
     Set the default cache directory to a temporary directory during tests.
 
@@ -35,7 +23,6 @@ def clean_parso_cache(request):
     tmp = tempfile.mkdtemp(prefix='parso-test-')
     cache._default_cache_path = tmp
 
-    @request.addfinalizer
-    def restore():
+    yield
     cache._default_cache_path = old
     shutil.rmtree(tmp)

tox.ini

@@ -2,7 +2,8 @@
 envlist = py26, py27, py33, py34, py35, py36
 [testenv]
 deps =
-    pytest>=2.3.5
+    pytest>=3.0.7
+# For --lf and --ff.
     pytest-cache
 setenv =
 # https://github.com/tomchristie/django-rest-framework/issues/1957