VSCode keeps complaining there is no "process.env"

I have a file test/test.ts which is as simple as one line:

process.env["NODE_ENV"] = 'test';

My VSCode complains that it cannot find 'process':

Cannot find name 'process'. Do you need to install type definitions for node? Try npm i @types/node.ts(2580)

However, when I run the Typescript compiler tsc test/test.ts is happy with the file without any error.

Of cource I have installed @types/node, but VSCode is still complaining. How can I fix that?