[Core] Consolidate prompt arguments to LLM engines (#4328)

Co-authored-by: Roger Wang <ywang@roblox.com>

tests/test_inputs.py

@@ -0,0 +1,53 @@
+from typing import List
+
+import pytest
+
+from vllm.inputs import parse_and_batch_prompt
+
+STRING_INPUTS = [
+    '',
+    'foo',
+    'foo bar',
+    'foo baz bar',
+    'foo bar qux baz',
+]
+
+TOKEN_INPUTS = [
+    [-1],
+    [1],
+    [1, 2],
+    [1, 3, 4],
+    [1, 2, 4, 3],
+]
+
+INPUTS_SLICES = [
+    slice(None, None, -1),
+    slice(None, None, 2),
+    slice(None, None, -2),
+]
+
+
+def test_parse_single_batch_empty():
+    with pytest.raises(ValueError, match="at least one prompt"):
+        parse_and_batch_prompt([])
+
+    with pytest.raises(ValueError, match="at least one prompt"):
+        parse_and_batch_prompt([[]])
+
+
+@pytest.mark.parametrize('string_input', STRING_INPUTS)
+def test_parse_single_batch_string_consistent(string_input: str):
+    assert parse_and_batch_prompt(string_input) \
+        == parse_and_batch_prompt([string_input])
+
+
+@pytest.mark.parametrize('token_input', TOKEN_INPUTS)
+def test_parse_single_batch_token_consistent(token_input: List[int]):
+    assert parse_and_batch_prompt(token_input) \
+        == parse_and_batch_prompt([token_input])
+
+
+@pytest.mark.parametrize('inputs_slice', INPUTS_SLICES)
+def test_parse_single_batch_string_slice(inputs_slice: slice):
+    assert parse_and_batch_prompt(STRING_INPUTS)[inputs_slice] \
+        == parse_and_batch_prompt(STRING_INPUTS[inputs_slice])