[Bugfix] Fix uninitialized decoded_token and add corresponding unit test. (#3195)

fastdeploy/entrypoints/llm.py

@@ -289,6 +289,10 @@ class LLM:
             self.llm_engine.add_requests(tasks, current_sampling_params, enable_thinking=enable_thinking)
         return req_ids
 
+    def _decode_token(self, token_id: int) -> str:
+        """Decodes a single token ID into its string representation."""
+        return self.llm_engine.data_processor.process_logprob_response([token_id], clean_up_tokenization_spaces=False)
+
     def _build_sample_logprobs(self, logprobs_lists: LogprobsLists, topk_logprobs: int) -> list[dict[int, Logprob]]:
         """
         Constructs a list of dictionaries mapping token IDs to Logprob objects,
@@ -322,8 +326,9 @@ class LLM:
             sliced_logprobs_lists = logprobs_lists.slice_columns(1, 1 + effective_topk_logprobs)
             result = []
             for token_ids, logprobs in zip(sliced_logprobs_lists.logprob_token_ids, sliced_logprobs_lists.logprobs):
+
                 logprob_dict = {
-                    token_id: Logprob(logprob=logprob, rank=i + 1, decoded_token=None)
+                    token_id: Logprob(logprob=logprob, rank=i + 1, decoded_token=self._decode_token(token_id))
                     for i, (token_id, logprob) in enumerate(zip(token_ids, logprobs))
                 }
                 result.append(logprob_dict)

test/entrypoints/openai/test_build_sample_logprobs.py

@@ -0,0 +1,78 @@
+import unittest
+from unittest.mock import MagicMock, patch
+
+from fastdeploy.entrypoints.llm import LLM
+from fastdeploy.worker.output import Logprob, LogprobsLists
+
+
+def get_patch_path(cls, method="__init__"):
+    return f"{cls.__module__}.{cls.__qualname__}.{method}"
+
+
+class TestBuildSampleLogprobs(unittest.TestCase):
+
+    def setUp(self):
+        """
+        Set up the test environment by creating an instance of the LLM class using Mock.
+        """
+        patch_llm = get_patch_path(LLM)
+        with patch(patch_llm, return_value=None):
+            self.llm = LLM()
+            # mock d data_processor
+            self.llm.llm_engine = MagicMock()
+            self.llm.llm_engine.data_processor.process_logprob_response.side_effect = (
+                lambda ids, **kwargs: f"token_{ids[0]}"
+            )
+
+    def test_build_sample_logprobs_basic(self):
+        """
+        Test case for building sample logprobs when `topk_logprobs` is valid.
+        """
+        logprob_token_ids = [[100, 101, 102]]
+        logprobs = [[-0.1, -0.5, -1.0]]
+        sampled_token_ranks = [0]
+
+        logprobs_lists = LogprobsLists(
+            logprob_token_ids=logprob_token_ids, logprobs=logprobs, sampled_token_ranks=sampled_token_ranks
+        )
+
+        result = self.llm._build_sample_logprobs(logprobs_lists, topk_logprobs=2)
+
+        expected = [
+            {
+                101: Logprob(logprob=-0.5, rank=1, decoded_token="token_101"),
+                102: Logprob(logprob=-1.0, rank=2, decoded_token="token_102"),
+            }
+        ]
+
+        self.assertEqual(result, expected)
+
+    def test_build_sample_logprobs_empty_input(self):
+        """
+        Test case where `logprob_token_ids` is empty.
+        """
+        logprobs_lists = MagicMock(spec=LogprobsLists)
+        logprobs_lists.logprob_token_ids = []
+        result = self.llm._build_sample_logprobs(logprobs_lists, topk_logprobs=2)
+        self.assertIsNone(result)
+
+    def test_build_sample_logprobs_invalid_topk(self):
+        """
+        Test case where `topk` value exceeds length of first element in `logprob_token_ids`.
+        """
+        logprobs_lists = MagicMock(spec=LogprobsLists)
+        logprobs_lists.logprob_token_ids = [[100]]
+        result = self.llm._build_sample_logprobs(logprobs_lists, topk_logprobs=2)
+        self.assertIsNone(result)
+
+    def test_decode_token(self):
+        """
+        Test case for decoding a single token ID.
+        """
+        token_id = 123
+        decoded = self.llm._decode_token(token_id)
+        self.assertEqual(decoded, "token_123")
+
+
+if __name__ == "__main__":
+    unittest.main()