Adds gc to reduce flakiness of base_trainer_test.

PiperOrigin-RevId: 389526906

official/core/base_trainer_test.py

@@ -14,6 +14,7 @@
 
 """Tests for tensorflow_models.core.trainers.trainer."""
 # pylint: disable=g-direct-tensorflow-import
+import gc
 import multiprocessing
 import os
 import sys
@@ -164,6 +165,13 @@ class TrainerTest(tf.test.TestCase, parameterized.TestCase):
                 }
             })))
 
+  def tearDown(self):
+    gc.collect()
+    # This will only contain uncollectable garbage, i.e. reference cycles
+    # involving objects with __del__ defined.
+    self.assertEmpty(gc.garbage)
+    super().tearDown()
+
   def create_test_trainer(self, config, model_dir=None, task=None):
     task = task or mock_task.MockTask(config.task, logging_dir=model_dir)
     ckpt_exporter = train_lib.maybe_create_best_ckpt_exporter(config, model_dir)