[Speculative decoding] Adding configuration object for speculative decoding (#3706)

Co-authored-by: Lily Liu <lilyliupku@gmail.com>

tests/spec_decode/e2e/test_correctness.py

@@ -0,0 +1,50 @@
+import pytest
+
+from vllm import SamplingParams
+
+
+@pytest.mark.parametrize(
+    "common_llm_kwargs",
+    [{
+        # Use a small model for a fast test.
+        "model": "facebook/opt-125m",
+        "speculative_model": "facebook/opt-125m",
+        "num_speculative_tokens": 5,
+
+        # Required for spec decode.
+        "use_v2_block_manager": True
+    }])
+@pytest.mark.parametrize("per_test_common_llm_kwargs", [{}])
+@pytest.mark.parametrize("test_llm_kwargs", [{}])
+@pytest.mark.parametrize("seed", [1])
+def test_spec_decode_config(test_llm_generator):
+    output_len = 1024
+    temperature = 0.0
+
+    prompts = [
+        "Hello, my name is",
+        "The president of the United States is",
+        "The capital of France is",
+        "The future of AI is",
+    ]
+
+    sampling_params = SamplingParams(
+        max_tokens=output_len,
+        ignore_eos=True,
+        temperature=temperature,
+    )
+
+    with pytest.raises(
+            AssertionError,
+            match="Speculative decoding not yet supported for GPU backend"):
+        get_token_ids_from_llm_generator(test_llm_generator, prompts,
+                                         sampling_params)
+
+
+def get_token_ids_from_llm_generator(llm_generator, prompts, sampling_params):
+    for llm in llm_generator:
+        outputs = llm.generate(prompts, sampling_params, use_tqdm=True)
+        token_ids = [output.outputs[0].token_ids for output in outputs]
+        del llm
+
+    return token_ids