test: rewrite regression test to call shorten_message_to_fit_limit directly

tests/litellm_utils_tests/test_utils.py

@@ -288,40 +288,18 @@ def test_trimming_with_model_cost_max_input_tokens(model):
 
 
 def test_shorten_message_content_never_grows():
-    """Regression test: shorten_message_to_fit_limit must never make content longer.
-
-    Bug: when half_length==0, content[-0:] == content[0:] (entire string) due to
-    Python's -0 == 0 identity, so trimmed = '' + '..' + full_content was longer
-    than the original.  This caused the loop to grow content on every subsequent
-    iteration instead of shrinking it.
-    """
-    from litellm.utils import get_token_count
-    from litellm.constants import MAX_TOKEN_TRIMMING_ATTEMPTS
+    """Regression test: shorten_message_to_fit_limit must never make content longer."""
+    from litellm.utils import shorten_message_to_fit_limit
 
     content = "hello world this is a moderately long message"
-    msg_copy = {"role": "user", "content": content}
-    max_len_seen = len(content)
-    tokens_needed = 1
-    model = None
+    message = {"role": "user", "content": content}
+    original_len = len(content)
 
-    for _ in range(MAX_TOKEN_TRIMMING_ATTEMPTS):
-        total_tokens = get_token_count([msg_copy], model)
-        if total_tokens <= tokens_needed:
-            break
-        ratio = tokens_needed / total_tokens
-        new_length = max(0, int(len(msg_copy["content"]) * ratio) - 1)
-        half_length = new_length // 2
-        if half_length == 0:
-            trimmed = msg_copy["content"][:new_length]
-        else:
-            c = msg_copy["content"]
-            trimmed = c[:half_length] + ".." + c[-half_length:]
-        assert len(trimmed) <= max_len_seen, (
-            f"Content grew from {max_len_seen} to {len(trimmed)} chars — "
-            "half_length==0 guard is missing"
-        )
-        max_len_seen = len(trimmed)
-        msg_copy["content"] = trimmed
+    result = shorten_message_to_fit_limit(message, tokens_needed=1, model=None)
+    assert len(result["content"]) <= original_len, (
+        f"Content grew from {original_len} to {len(result['content'])} chars — "
+        "half_length==0 guard is missing or broken"
+    )
 
 
 def test_trimming_with_untokenizable_field(caplog: pytest.LogCaptureFixture) -> None: