When you use mocha with flag --watch on typescript you need to set .mocharc.json file on root folder of project to specify for mocha watch .ts files; Otherwise the terminal will spawn in the first run but will not restart when you save the file.
// .mocharc.json
{
"extension": [
"ts"
],
"spec": "__tests__/**/*.spec.ts",
"watch": true
}
# Simple run on terminal
yarn ts-mocha