Fix GPU OOM for `mistral.py::Mask4DTestHard` (#31212)

* build

* build

* build

* build

---------
Co-authored-by: ydshieh <ydshieh@users.noreply.github.com>

tests/models/mistral/test_modeling_mistral.py

@@ -734,15 +734,24 @@ class MistralIntegrationTest(unittest.TestCase):
 @slow
 @require_torch_gpu
 class Mask4DTestHard(unittest.TestCase):
+    model_name = "mistralai/Mistral-7B-v0.1"
+    _model = None
+
     def tearDown(self):
         gc.collect()
         torch.cuda.empty_cache()
 
+    @property
+    def model(self):
+        if self.__class__._model is None:
+            self.__class__._model = MistralForCausalLM.from_pretrained(
+                self.model_name, torch_dtype=self.model_dtype
+            ).to(torch_device)
+        return self.__class__._model
+
     def setUp(self):
-        model_name = "mistralai/Mistral-7B-v0.1"
-        self.model_dtype = torch.float32
-        self.tokenizer = AutoTokenizer.from_pretrained(model_name, use_fast=False)
-        self.model = MistralForCausalLM.from_pretrained(model_name, torch_dtype=self.model_dtype).to(torch_device)
+        self.model_dtype = torch.float16
+        self.tokenizer = AutoTokenizer.from_pretrained(self.model_name, use_fast=False)
 
     def get_test_data(self):
         template = "my favorite {}"