diff --git a/conftest.py b/conftest.py
new file mode 100644
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--- /dev/null
+++ b/conftest.py
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+import tempfile
+import shutil
+
+import pytest
+
+import jedi
+
+collect_ignore = ["setup.py"]
+
+
+# The following hooks (pytest_configure, pytest_unconfigure) are used
+# to modify `jedi.settings.cache_directory` because `clean_jedi_cache`
+# has no effect during doctests.  Without these hooks, doctests uses
+# user's cache (e.g., ~/.cache/jedi/).  We should remove this
+# workaround once the problem is fixed in py.test.
+#
+# See:
+# - https://github.com/davidhalter/jedi/pull/168
+# - https://bitbucket.org/hpk42/pytest/issue/275/
+
+jedi_cache_directory_orig = None
+jedi_cache_directory_temp = None
+
+
+def pytest_addoption(parser):
+    parser.addoption("--jedi-debug", "-D", action='store_true',
+                     help="Enables Jedi's debug output.")
+
+    parser.addoption("--warning-is-error", action='store_true',
+                     help="Warnings are treated as errors.")
+
+
+def pytest_configure(config):
+    global jedi_cache_directory_orig, jedi_cache_directory_temp
+    jedi_cache_directory_orig = jedi.settings.cache_directory
+    jedi_cache_directory_temp = tempfile.mkdtemp(prefix='jedi-test-')
+    jedi.settings.cache_directory = jedi_cache_directory_temp
+
+    if config.option.jedi_debug:
+        jedi.set_debug_function()
+
+    if config.option.warning_is_error:
+        import warnings
+        warnings.simplefilter("error")
+
+
+def pytest_unconfigure(config):
+    global jedi_cache_directory_orig, jedi_cache_directory_temp
+    jedi.settings.cache_directory = jedi_cache_directory_orig
+    shutil.rmtree(jedi_cache_directory_temp)
+
+
+@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.
+    """
+    from jedi import 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)