[Misc] Fix skipped max-model-len validation when deriving max model length from tokenizer config (#19660)

Signed-off-by: Ye (Charlotte) Qi <yeq@meta.com>

tests/test_config.py

@@ -438,3 +438,31 @@ def test_load_config_pt_load_map_location(pt_load_map_location):
     config = VllmConfig(load_config=load_config)
 
     assert config.load_config.pt_load_map_location == pt_load_map_location
+
+
+@pytest.mark.parametrize(
+    ("model_id", "max_model_len", "expected_max_len", "should_raise"), [
+        ("BAAI/bge-reranker-base", None, 512, False),
+        ("BAAI/bge-reranker-base", 256, 256, False),
+        ("BAAI/bge-reranker-base", 513, 512, True),
+    ])
+def test_get_and_verify_max_len(model_id, max_model_len, expected_max_len,
+                                should_raise):
+    """Test get_and_verify_max_len with different configurations."""
+    model_config = ModelConfig(
+        model_id,
+        task="auto",
+        tokenizer=model_id,
+        tokenizer_mode="auto",
+        trust_remote_code=False,
+        seed=0,
+        dtype="float16",
+        revision=None,
+    )
+
+    if should_raise:
+        with pytest.raises(ValueError):
+            model_config.get_and_verify_max_len(max_model_len)
+    else:
+        actual_max_len = model_config.get_and_verify_max_len(max_model_len)
+        assert actual_max_len == expected_max_len