[Core] remove cupy dependency (#3625)

tests/distributed/test_basic_distributed_correctness.py

@@ -1,13 +1,22 @@
 """Compare the outputs of HF and distributed vLLM when using greedy sampling.
-
-Run `pytest tests/distributed/test_basic_distributed_correctness.py --forked`.
+vLLM will allocate all the available memory, so we need to run the tests one
+by one. The solution is to pass arguments (model name) by environment
+variables.
+Run:
+```sh
+TEST_DIST_MODEL=facebook/opt-125m pytest \
+    test_basic_distributed_correctness.py
+TEST_DIST_MODEL=meta-llama/Llama-2-7b-hf \
+    test_basic_distributed_correctness.py
+```
 """
+import os
+
 import pytest
 import torch
 
 MODELS = [
-    "facebook/opt-125m",
-    "meta-llama/Llama-2-7b-hf",
+    os.environ["TEST_DIST_MODEL"],
 ]