add a test

Author: sayakpaul

tests/quantization/bnb/test_4bit.py

@@ -752,6 +752,20 @@ def test_lora_loading(self):
         max_diff = numpy_cosine_similarity_distance(expected_slice, out_slice)
         self.assertTrue(max_diff < 1e-3, msg=f"{out_slice=} != {expected_slice=}")
 
+    def test_loading_lora_with_incorrect_dtype_raises_error(self):
+        self.tearDown()
+        model_dtype = torch.bfloat16
+        #  https://huggingface.co/eramth/flux-4bit/blob/main/transformer/config.json#L23
+        actual_dtype = torch.float16
+        self.pipeline_4bit = FluxControlPipeline.from_pretrained("eramth/flux-4bit", torch_dtype=torch.bfloat16)
+        self.pipeline_4bit.enable_model_cpu_offload()
+        with self.assertRaises(ValueError) as err_context:
+            self.pipeline_4bit.load_lora_weights("black-forest-labs/FLUX.1-Canny-dev-lora")
+        assert (
+            f"Model is in {model_dtype} dtype while the current module weight will be dequantized to {actual_dtype} dtype."
+            in str(err_context.exception)
+        )
+
 
 @slow
 class BaseBnb4BitSerializationTests(Base4bitTests):