Support more tests than just startup

It looks like I will need tests that some of the more interesting
packages actually work, not just build.

tests.el

@@ -0,0 +1,38 @@
+;; -*- lexical-binding: t; -*-
+
+;; Copyright 2024 Google LLC
+;;
+;; Licensed under the Apache License, Version 2.0 (the "License");
+;; you may not use this file except in compliance with the License.
+;; You may obtain a copy of the License at
+;;
+;;     http://www.apache.org/licenses/LICENSE-2.0
+;;
+;; Unless required by applicable law or agreed to in writing, software
+;; distributed under the License is distributed on an "AS IS" BASIS,
+;; WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+;; See the License for the specific language governing permissions and
+;; limitations under the License.
+
+;; Config file for integration tests.
+;;
+;; This tries to hook into startup as late as possible, write a sign of life
+;; (currently a string written to $out), and then exits.
+
+(defun test-minimal ()
+  ;; The minimal test is a noop.
+  )
+
+(defun test-doom ()
+  (let* ((out (getenv "out"))
+         (test (intern-soft (format "test-%s" (getenv "testName"))))
+         (result (condition-case err
+                     (funcall test)
+                   (error
+                    (format "%s failed: %s" test err))
+                   (:success
+                    "Doom functions"))))
+    (write-region result nil out nil nil nil 'mustbenew))
+  (kill-emacs))
+
+(add-hook 'doom-after-init-hook 'test-doom)