[Spec] Clean up draft-window-size handling; extract spec arg setup to arg_groups (#25424)

test/registered/unit/server_args/test_server_args.py

@@ -3,6 +3,7 @@ import tempfile
 import unittest
 from unittest.mock import MagicMock, patch
 
+from sglang.srt.arg_groups.speculative_hook import handle_speculative_decoding
 from sglang.srt.server_args import PortArgs, ServerArgs, prepare_server_args
 from sglang.test.ci.ci_register import register_cpu_ci
 from sglang.test.test_utils import (
@@ -497,21 +498,23 @@ class TestNgramExternalSamArgs(CustomTestCase):
         return args
 
     def test_external_sam_budget_must_fit_draft_budget(self):
+        args = self._make_dummy_ngram_args(
+            speculative_num_draft_tokens=4,
+            speculative_ngram_external_corpus_path="/tmp/ngram-corpus.jsonl",
+            speculative_ngram_external_sam_budget=4,
+        )
         with self.assertRaises(ValueError) as context:
-            self._make_dummy_ngram_args(
-                speculative_num_draft_tokens=4,
-                speculative_ngram_external_corpus_path="/tmp/ngram-corpus.jsonl",
-                speculative_ngram_external_sam_budget=4,
-            )._handle_speculative_decoding()
+            handle_speculative_decoding(args)
         self.assertIn("speculative_num_draft_tokens - 1", str(context.exception))
 
     def test_external_corpus_max_tokens_must_be_positive(self):
+        args = self._make_dummy_ngram_args(
+            speculative_ngram_external_corpus_path="/tmp/ngram-corpus.jsonl",
+            speculative_ngram_external_sam_budget=2,
+            speculative_ngram_external_corpus_max_tokens=0,
+        )
         with self.assertRaises(ValueError) as context:
-            self._make_dummy_ngram_args(
-                speculative_ngram_external_corpus_path="/tmp/ngram-corpus.jsonl",
-                speculative_ngram_external_sam_budget=2,
-                speculative_ngram_external_corpus_max_tokens=0,
-            )._handle_speculative_decoding()
+            handle_speculative_decoding(args)
         self.assertIn("external-corpus-max-tokens", str(context.exception))