When a story is created and that story moves from open to the designer status then automatically create 3 types of sub-task like
1st sub-task name is the design subtask
2nd sub-task name is coding "
3rd sub-task name is a tester "
In the story, I used a single-user custom field for the designer, coding, and tester.
I used a validator like while a story moves from open to design, please mention the designer name, coder name, and tester name.
when the created story reaches design status the 1st design sub-task will automatically assign to the designer and the remaining sub-task will not assign to 2 sub-tasks
when the designer completes the 1st sub-task then the 2nd sub-task will assign to the coder automatically and the parent story also moves to the coding status. He completes the coding sub-task then the 3rd sub-task will assign automatically to the tester and the parent also moves to the tester status.
And last, when these three subtasks are completed then the parent-like story also will reach to done status