[Bugfix] Make MM batching more robust (#33817)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

tests/multimodal/test_inputs.py

@@ -0,0 +1,46 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+import pytest
+import torch
+
+from vllm.multimodal.inputs import PlaceholderRange
+
+
+@pytest.mark.parametrize(
+    "is_embed,expected",
+    [
+        (None, 5),
+        (torch.tensor([True, True, True, True, True]), 5),
+        (torch.tensor([False, False, False, False, False]), 0),
+        (torch.tensor([True, False, True, False, True]), 3),
+        (torch.tensor([True]), 1),
+    ],
+)
+def test_placeholder_range_get_num_embeds(is_embed, expected):
+    length = len(is_embed) if is_embed is not None else 5
+    pr = PlaceholderRange(offset=0, length=length, is_embed=is_embed)
+    assert pr.get_num_embeds == expected
+
+
+@pytest.mark.parametrize(
+    "is_embed,expected",
+    [
+        (None, None),
+        (
+            torch.tensor([False, True, False, True, True]),
+            torch.tensor([0, 1, 1, 2, 3]),
+        ),
+        (torch.tensor([True, True, True]), torch.tensor([1, 2, 3])),
+    ],
+)
+def test_placeholder_range_embeds_cumsum(is_embed, expected):
+    length = len(is_embed) if is_embed is not None else 5
+    pr = PlaceholderRange(offset=0, length=length, is_embed=is_embed)
+
+    if expected is None:
+        assert pr.embeds_cumsum is None
+        return
+
+    assert torch.equal(pr.embeds_cumsum, expected)
+    # cached_property should return the same object on repeated access
+    assert pr.embeds_cumsum is pr.embeds_cumsum