Newbies take note:

• First use Debug|Open Configurations to generate and show a .vscode/launch.json file for your project
• Insert the magic snippet in the "configurations": [...] array. -i means --runInBand(no parallelism). Comment out "envFile" if you have no .env file. If you use ts-jest, comment out "preLaunchTask" and "outFiles"seems to have no effect.
• Click debug icon on the left and select “Jest tests”. Perhaps set a breakpoint and press F5 to start (Debug|Start Debugging)
• Personally I can’t set breakpoints in my ts files (maybe ts-jest doesn’t provide source maps to the debugger in the right way?) Also, Jest doesn’t seem to produce its output until all tests have finished. Sigh.