Global app server variable for tests

[albertcito]

I tried to do it configuring globalSetup with a function to call Express server and save it in global variable. It prints this error:

SyntaxError: Cannot use import statement outside a module

It's a Jest issue that will be solved https://stackoverflow.com/questions/60372790/node-v13-jest-es6-native-support-for-modules-without-babel-or-esm/61653104#61653104

When it's ready, I'll try again to use the global variable in different files.