Use custom plugin to download test data early

python/cuml/tests/conftest.py

@@ -264,6 +264,8 @@ def pytest_configure(config):
     else:
         hypothesis.settings.load_profile("unit")
 
+    config.pluginmanager.register(DownloadDataPlugin(), "download_data")
+
 
 def pytest_pyfunc_call(pyfuncitem):
     """Skip tests that require the cudf.pandas accelerator.
@@ -403,6 +405,23 @@ def random_seed(request):
 # =============================================================================
 
 
+class DownloadDataPlugin:
+    """Download data before workers are spawned.
+
+    This avoids downloading data in each worker, which can lead to races.
+    """
+
+    def pytest_configure(self, config):
+        if not hasattr(config, "workerinput"):
+            # We're in the controller process, not a worker. Let's fetch all
+            # the datasets we might use.
+            fetch_20newsgroups()
+            fetch_california_housing()
+            datasets.load_digits()
+            datasets.load_diabetes()
+            datasets.load_breast_cancer()
+
+
 def dataset_fetch_retry(func, attempts=3, min_wait=1, max_wait=10):
     """Decorator for retrying dataset fetching operations with exponential backoff.