How it works

Probes are inserted into code files of software under test that QA wants to get test coverage from. Probes are inserted automatically by instrument_client python script. The script talks to instrument_server that typically runs on port 5000. The client detects all source files within specified in config source root, injects probes and uploads list of them to the server.

After that, the tool has a list of sources along with contents and executable lines.

The probes are simple lines of code that, simply put, call server's api with details like line unique ID or index number. So when probe code is executed (hopefully via your testing activity), it sends info to server and server knows which line was just executed.

Knowing how many lines are there in overall, it can be determined what percentage of executable lines, were triggered lines. This is test coverage.