File Modifications During Test Execution

[gunar]

I'd like to request a feature / bugfix. When tests are undergoing, and files are changed mid run, ptw should queue another run immediately next.

Actual vs Expected:

  1. I change a file
  2. `ptw` identifies it and triggers a test run
  3. Tests start running (integration tests take longer)
  4. I change another file before tests finish running
  5. `ptw` logs `[ptw] ./path/myfile.py modified`
- 6. `ptw` finishes the test run and waits for new file changes
+ 6. `ptw` immediately starts another test run since files were changed during the previous run

Bonus: ptw could stop the current test run and start from scratch (i.e. no need to wait for the previous run to finish).

[olzhasar]

The idea looks reasonable (as long as the behavior can be disabled in case things go wrong).

So we essentially need to keep a reference to the current child process and "kill" it whenever a new event comes in while the child is still running.

@gunar @mecampbellsoup, do you guys want to play around with a possible implementation?