Run py.test in clean cache directory

And finally remove XDG_CACHE_HOME=... in tox.ini.

pytest.ini

@@ -1,2 +1,7 @@
 [pytest]
 addopts = --assert=plain
+
+# Activate `clean_jedi_cache` fixture for all tests.  This should be
+# fine as long as we are using `clean_jedi_cache` as a session scoped
+# fixture.
+usefixtures = clean_jedi_cache

test/conftest.py

@@ -1,4 +1,8 @@
 import os
+import shutil
+import tempfile
+
+import pytest
 
 from . import base
 from . import run
@@ -57,3 +61,25 @@ def pytest_generate_tests(metafunc):
         metafunc.parametrize(
             'refactor_case',
             refactor.collect_dir_tests(base_dir, test_files))
+
+
+@pytest.fixture(scope='session')
+def clean_jedi_cache(request):
+    """
+    Set `jedi.settings.cache_directory` to a temporary directory during test.
+
+    Note that you can't use built-in `tmpdir` and `monkeypatch`
+    fixture here because their scope is 'function', which is not used
+    in 'session' scope fixture.
+
+    This fixture is activated in ../pytest.ini.
+    """
+    settings = base.jedi.settings
+    old = settings.cache_directory
+    tmp = tempfile.mkdtemp(prefix='jedi-test-')
+    settings.cache_directory = tmp
+
+    @request.addfinalizer
+    def restore():
+        settings.cache_directory = old
+        shutil.rmtree(tmp)

test/test_integration.py

@@ -1,6 +1,8 @@
 import os
 import re
 
+import pytest
+
 from . import base
 from .run import \
     TEST_COMPLETIONS, TEST_DEFINITIONS, TEST_ASSIGNMENTS, TEST_USAGES

tox.ini

@@ -1,8 +1,6 @@
 [tox]
 envlist = py25, py26, py27, py32
 [testenv]
-setenv =
-    XDG_CACHE_HOME={envtmpdir}/cache
 deps =
     pytest
 commands =