fix organize agent's history messages without recalculating tokens (#4324)

Co-authored-by: chenyongzhao <chenyz@mama.cn>

api/tests/unit_tests/core/prompt/test_agent_history_prompt_transform.py

@@ -0,0 +1,77 @@
+from unittest.mock import MagicMock
+
+from core.app.entities.app_invoke_entities import (
+    ModelConfigWithCredentialsEntity,
+)
+from core.entities.provider_configuration import ProviderModelBundle
+from core.memory.token_buffer_memory import TokenBufferMemory
+from core.model_runtime.entities.message_entities import (
+    AssistantPromptMessage,
+    SystemPromptMessage,
+    ToolPromptMessage,
+    UserPromptMessage,
+)
+from core.model_runtime.model_providers.__base.large_language_model import LargeLanguageModel
+from core.prompt.agent_history_prompt_transform import AgentHistoryPromptTransform
+from models.model import Conversation
+
+
+def test_get_prompt():
+    prompt_messages = [
+        SystemPromptMessage(content='System Template'),
+        UserPromptMessage(content='User Query'),
+    ]
+    history_messages = [
+        SystemPromptMessage(content='System Prompt 1'),
+        UserPromptMessage(content='User Prompt 1'),
+        AssistantPromptMessage(content='Assistant Thought 1'),
+        ToolPromptMessage(content='Tool 1-1', name='Tool 1-1', tool_call_id='1'),
+        ToolPromptMessage(content='Tool 1-2', name='Tool 1-2', tool_call_id='2'),
+        SystemPromptMessage(content='System Prompt 2'),
+        UserPromptMessage(content='User Prompt 2'),
+        AssistantPromptMessage(content='Assistant Thought 2'),
+        ToolPromptMessage(content='Tool 2-1', name='Tool 2-1', tool_call_id='3'),
+        ToolPromptMessage(content='Tool 2-2', name='Tool 2-2', tool_call_id='4'),
+        UserPromptMessage(content='User Prompt 3'),
+        AssistantPromptMessage(content='Assistant Thought 3'),
+    ]
+
+    # use message number instead of token for testing
+    def side_effect_get_num_tokens(*args):
+        return len(args[2])
+    large_language_model_mock = MagicMock(spec=LargeLanguageModel)
+    large_language_model_mock.get_num_tokens = MagicMock(side_effect=side_effect_get_num_tokens)
+
+    provider_model_bundle_mock = MagicMock(spec=ProviderModelBundle)
+    provider_model_bundle_mock.model_type_instance = large_language_model_mock
+
+    model_config_mock = MagicMock(spec=ModelConfigWithCredentialsEntity)
+    model_config_mock.model = 'openai'
+    model_config_mock.credentials = {}
+    model_config_mock.provider_model_bundle = provider_model_bundle_mock
+
+    memory = TokenBufferMemory(
+        conversation=Conversation(),
+        model_instance=model_config_mock
+    )
+
+    transform = AgentHistoryPromptTransform(
+        model_config=model_config_mock,
+        prompt_messages=prompt_messages,
+        history_messages=history_messages,
+        memory=memory
+    )
+
+    max_token_limit = 5
+    transform._calculate_rest_token = MagicMock(return_value=max_token_limit)
+    result = transform.get_prompt()
+
+    assert len(result) <= max_token_limit
+    assert len(result) == 4
+
+    max_token_limit = 20
+    transform._calculate_rest_token = MagicMock(return_value=max_token_limit)
+    result = transform.get_prompt()
+
+    assert len(result) <= max_token_limit
+    assert len(result) == 12