Automate testing of serial-device example

Signed-off-by: Nick Spinale <[email protected]>

hacking/nix/scope/world/instances/default.nix

@@ -346,15 +346,27 @@ in rec {
         };
       });
 
-      serial-device = maybe (haveFullRuntime && hostPlatform.isAarch) (mkInstance {
+      serial-device = maybe (haveFullRuntime && hostPlatform.isAarch) (lib.fix (self: mkInstance {
         rootTask = mkTask {
           rootCrate = crates.serial-device;
           release = false;
         };
         extraPlatformArgs = lib.optionalAttrs canSimulate {
           canAutomateSimply = true;
         };
-      });
+      } // lib.optionalAttrs canSimulate rec {
+        automate =
+          let
+            py = buildPackages.python3.withPackages (pkgs: [
+              pkgs.pexpect
+            ]);
+          in
+            writeScript "automate" ''
+              #!${buildPackages.runtimeShell}
+              set -eu
+              ${py}/bin/python3 ${./test-automation-scripts/serial-device.py} ${self.simulate}
+            '';
+      }));
 
       spawn-thread = maybe haveFullRuntime (mkInstance {
         rootTask = mkTask {

hacking/nix/scope/world/instances/test-automation-scripts/serial-device.py

@@ -0,0 +1,28 @@
+#
+# Copyright 2023, Colias Group, LLC
+#
+# SPDX-License-Identifier: BSD-2-Clause
+#
+
+import sys
+import time
+import argparse
+import pexpect
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument('simulate')
+    args = parser.parse_args()
+    run(args)
+
+def run(args):
+    child = pexpect.spawn(args.simulate, encoding='utf-8')
+    child.logfile = sys.stdout
+    child.expect('echo> ', timeout=5)
+    time.sleep(1)
+    child.send('xxx')
+    child.expect('\[x\]\[x\]\[x\]', timeout=5)
+    print()
+
+if __name__ == '__main__':
+    main()