Before this change, other agent's reply with thought will still be inserted in the outgoing LlmRequest due to the wrong `else` statement for calling all other type of part.
This commit also refactors test_contents.py to be behavior-oriented tests, instead of implementation-oriented, and add more test cases to cover expected scenarios.
The tests are divided into the following files with different focus:
- test_contents.py: covers the basic logic of event filter;
- test_contents_branch.py: covers the behavior related to branch, which takes effect when ParallelAgent is used.
- test_contents_other_agent.py: covers the retelling behavior to include other agents' reply as context for the current agent.
- test_contents_function.py: covers the function_call/function_response rearrangement logic mainly for `LongRunningFunctionTool`.
PiperOrigin-RevId: 802759821
George WealeandCopybara-Service
Wei Sun (Jack)andCopybara-Service