Use netcat check to wait for python

script/run-axe.sh

@@ -3,14 +3,19 @@ set -euo pipefail
 
 # start a web server in the background and tear it down when exiting
 ./script/serve.sh public &
-
-# Wait for the python server to launch since we're launching it async
-sleep 3
-
 SERVER_PID=$!
 cleanup() {
     kill "$SERVER_PID"
 }
 trap cleanup EXIT INT
 
+# Wait for the python server to launch since we're launching it async
+>&2 echo "Waiting for web server to launch on port 8000..."
+while ! nc -z localhost 8000 &>/dev/null; do
+  >&2 echo "Web server not up yet... waiting some more..."
+  sleep 1
+done
+>&2 echo "Web server launched"
+
+
 node script/axe-puppeteer.js http://localhost:8000

shell.nix

@@ -31,6 +31,7 @@ stdenv.mkDerivation {
 
     # stuff we need for running builds in a `nix-shell --pure` environment.
     which
+    netcat-gnu
   ] ++ lib.optionals stdenv.isLinux [ pkgs.fsatrace pkgs.strace pkgs.cacert ];
 
   # environment variables