This turned up in working the CI for #129.
Turns out pexpect (and thus sensibly pytest) doesn't support spawn() on Windows so we have no way to know with the current testing situation if the debugger works 100%. I'm going to try out the popen_spawn stuff, but not holding my breath.
If anyone has ideas on how to make this work please speak up.
Ideally a collaborator eventually comes along who can help with this.