In the Meson build system's test harness, a single Ctrl-C terminates the longest running test with a SIGTERM; while three Ctrl-C in a second interrupt the whole run as if you sent the harness a SIGTERM. This was done because it's not uncommon that there are hundreds of tests left to run and you have seen what you want, and it's useful to have an intuitive shortcut for that case.

However, in both cases it's a clean shutdown, all running are terminated and the test report is printed.