diff --git a/swh/core/pytest_plugin.py b/swh/core/pytest_plugin.py
--- a/swh/core/pytest_plugin.py
+++ b/swh/core/pytest_plugin.py
@@ -118,7 +118,7 @@
     return fd
 
 
-@pytest.fixture
+@pytest.fixture(scope="session")
 def datadir(request: pytest.FixtureRequest) -> str:
     """By default, returns the test directory's data directory.