[UnitTest] Use pytest's scope='session' for tvm.testing.parameter

Prior to this commit, the `tvm.testing.parameter` utility defined a
fixture with the default `scope="function"`.  However, this prevents
use of these parameters as arguments for other fixtures that are
themselves cached using pytest.  Since these are parameters, not large
values that would be expensive to compute, there is no downside to
caching them at the pytest level.

This commit updates the scope of fixtures generated using
`tvm.testing.parameter` to use `scope="session"` instead of the
default `scope="function"`.

Author: Lunderberg

python/tvm/testing/utils.py

@@ -1447,7 +1447,7 @@ def parameter(*values, ids=None, by_dict=None):
 
     # Optional cls parameter in case a parameter is defined inside a
     # class scope.
-    @pytest.fixture(params=values, ids=ids)
+    @pytest.fixture(params=values, ids=ids, scope="session")
     def as_fixture(*_cls, request):
         return request.param
 

tests/python/testing/test_tvm_testing_features.py

@@ -290,5 +290,16 @@ def test_uses_deepcopy(self, fixture_with_deepcopy):
         pass
 
 
+class TestPytestCache:
+    param = tvm.testing.parameter(1, 2, 3)
+
+    @pytest.fixture(scope="class")
+    def cached_fixture(self, param):
+        return param * param
+
+    def test_uses_cached_fixture(self, param, cached_fixture):
+        assert cached_fixture == param * param
+
+
 if __name__ == "__main__":
     tvm.testing.main()