Add test to compare encoder inference on input with and without padding

test/models/test_transformers.py

@@ -0,0 +1,51 @@
+import torch
+
+from ..common.parameterized_utils import nested_params
+from ..common.torchtext_test_case import TorchtextTestCase
+
+
+class TestTransformers(TorchtextTestCase):
+    @nested_params(
+        [True, False],
+        [True, False],
+    )
+    def test_padded_input_inference(self, with_no_grad, return_all_layers):
+        """test transformerencoder inference same with and without padding"""
+        from torchtext.models import RobertaEncoderConf, RobertaModel
+
+        def encoder_inference(encoder, input_lst, with_no_grad):
+            if with_no_grad:
+                with torch.no_grad():
+                    res = [encoder(eval_input) for eval_input in input_lst]
+            else:
+                res = [encoder(eval_input) for eval_input in input_lst]
+            return res
+
+        # Roberta config except for less layers (2 instead of 12)
+        pad_idx = 1
+        encoder_conf = RobertaEncoderConf(
+            vocab_size=250002,
+            embedding_dim=768,
+            ffn_dimension=3072,
+            padding_idx=pad_idx,
+            max_seq_len=514,
+            num_attention_heads=12,
+            num_encoder_layers=2,
+            dropout=0.1,
+            scaling=None,
+            normalize_before=False,
+        )
+        model = RobertaModel(encoder_conf)
+        model = model.eval()
+        # TODO: make return_all_layers a property of RobertaEncoderConf so it can be passed as arg
+        model.encoder.transformer.return_all_layers = return_all_layers
+
+        # result from converting string "some text" to tensor using xlmr_base embeddings
+        input_no_pad = torch.Tensor([[0, 3060, 7986, 2]]).to(torch.int)
+        data_len = input_no_pad.shape[1]  # sequence length of non-pad data
+        # add two padding tokens to input_no_pad
+        input_pad = torch.Tensor([[0, 3060, 7986, 2, pad_idx, pad_idx]]).to(torch.int)
+        input_lst = [input_no_pad, input_pad]
+
+        output_no_pad, output_pad = encoder_inference(model, input_lst, with_no_grad)
+        torch.testing.assert_close(output_no_pad, output_pad[:, :data_len, :])