Tests: improve memory usage (#1147)

tests/conftest.py

+import gc
+
 import pytest
 import torch
 
@@ -20,6 +22,13 @@ def pytest_runtest_call(item):
         raise
 
 
+@pytest.hookimpl(trylast=True)
+def pytest_runtest_teardown(item, nextitem):
+    gc.collect()
+    if torch.cuda.is_available():
+        torch.cuda.empty_cache()
+
+
 @pytest.fixture(scope="session")
 def requires_cuda() -> bool:
     cuda_available = torch.cuda.is_available()