[ML TTK] Test coverage for participants endpoints #4271
Description
Create tests for all /participants endpoints.
- POST /participants
- PUT /participants/{ID}
- PUT /participants/{ID}/error
- POST /participants/{Type}/{ID}
- GET /participants/{Type}/{ID}
- PUT /participants/{Type}/{ID}
- DELETE /participants/{Type}/{ID}
- PUT /participants/{Type}/{ID}/error
- POST /participants/{Type}/{ID}/{SubId}
- GET /participants/{Type}/{ID}/{SubId}
- PUT /participants/{Type}/{ID}/{SubId}
- DELETE /participants/{Type}/{ID}/{SubId}
- PUT /participants/{Type}/{ID}/{SubId}/error