Cypress

You cannot use cypress directly with npm. You can either run it with steam-run or install the cypress package.

For example, put this shell.nix in the directory with your cypress tests:

{ pkgs ? import <nixpkgs> {} }:
  pkgs.mkShell {
    nativeBuildInputs = with pkgs; [
      nodejs
      cypress
    ];
}

You can then just run nix-shell --run "Cypress" to open the Cypress UI and then select your project.