### What problem does this PR solve?

cover [create session with chat
assistant](https://ragflow.io/docs/dev/http_api_reference#create-session-with-chat-assistant)
endpoints

### Type of change

- [x] add test cases

### What problem does this PR solve?

cover [create chat
assistant](https://ragflow.io/docs/v0.17.2/http_api_reference#create-chat-assistant)
endpoints

### Type of change

- [x] add test cases

### What problem does this PR solve?

 Refactor test fixtures and test cases

### Type of change

- [ ] Refactoring test cases

### What problem does this PR solve?

_Briefly describe what this PR aims to solve. Include background context
that will help reviewers understand the purpose of the PR._

### Type of change

- [x] update test cases

### What problem does this PR solve?

cover [download docments
endpoints](https://ragflow.io/docs/dev/http_api_reference#download-document)

### Type of change

- [x] add test cases

### What problem does this PR solve?

cover upload docments endpoints

### Type of change

- [x] add test cases