Playwright e2e under Nix

For projects that already have a Playwright e2e suite (typically under tests/) and need it to run locally on NixOS / pure-Nix hosts, where Playwright's bundled Chromium download depends on apt-get + sudo.

GitHub Actions CI is left untouched — apt-provided Chromium on Ubuntu runners is cheaper than spinning up a Nix devshell. This skill is for local runs (and Nix-based CI like Vira); GHA continues to use its own apt path.

Add a nixpkgs-latest flake input

In top-level flake.nix, add an independent pin so the Playwright rev moves on its own cadence (decoupled from the main nixpkgs your build uses):

inputs.nixpkgs-latest.url = "github:nixos/nixpkgs/nixpkgs-unstable";

tests/shell.nix

Self-contained. Reads the parent flake's lock to resolve nixpkgs-latest without needing a flake context:

let
  lock = builtins.fromJSON (builtins.readFile ../flake.lock);
  nixpkgsLocked = lock.nodes.nixpkgs-latest.locked;
  pkgs = import (builtins.fetchTree {
    type = "github";
    inherit (nixpkgsLocked) owner repo rev narHash;
  }) { };
in
pkgs.mkShell {
  packages = [ pkgs.nodejs ];
  PLAYWRIGHT_BROWSERS_PATH = "${pkgs.playwright-driver.browsers}";
  PLAYWRIGHT_SKIP_BROWSER_DOWNLOAD = "1";
}

Justfile recipe

e2e:
    nix-shell tests/shell.nix --run "cd tests && { [ -d node_modules ] || npm ci; } && npm test"

Critical version constraint

pkgs.playwright-driver version must match the playwright version in tests/package.json. Drift raises "browser revision X not found at <PLAYWRIGHT_BROWSERS_PATH>" at launch.

Bump both together:

1. nix flake update nixpkgs-latest
2. Match playwright in tests/package.json to the new driver version
3. npm install in tests/ to regenerate the lockfile

Reference

Pattern extracted from emanote#660.