[Test] Add ignore_eos test (#4519)

tests/samplers/test_ignore_eos.py

+"""Make sure ignore_eos works.
+
+Run `pytest tests/samplers/test_ignore_eos.py`.
+"""
+
+import pytest
+
+from vllm import SamplingParams
+
+MODELS = ["facebook/opt-125m"]
+
+
+@pytest.mark.parametrize("model", MODELS)
+@pytest.mark.parametrize("dtype", ["half"])
+@pytest.mark.parametrize("max_tokens", [1024])
+def test_beam_search_single_input(
+    vllm_runner,
+    example_prompts,
+    model: str,
+    dtype: str,
+    max_tokens: int,
+) -> None:
+    example_prompts = "1 + 1 is"
+
+    vllm_model = vllm_runner(model, dtype=dtype)
+    sampling_params = SamplingParams(max_tokens=max_tokens, ignore_eos=True)
+    ignore_eos_output = vllm_model.model.generate(
+        example_prompts, sampling_params=sampling_params)
+    print(len(ignore_eos_output[0].outputs[0].token_ids))
+    assert max_tokens - len(ignore_eos_output[0].outputs[0].token_ids) < 10
+    assert max_tokens - len(ignore_eos_output[0].outputs[0].token_ids) >= 0