nixos/tests: add basic test for services.atd

(cherry picked from commit 943730ff9b6b05c61ef75d7e2f3fae17d4cbdf4f)

(Fix trivial conflict in nixos/release.nix.)

nixos/release.nix

···
   # Run the tests for each platform.  You can run a test by doing
   # e.g. ‘nix-build -A tests.login.x86_64-linux’, or equivalently,
   # ‘nix-build tests/login.nix -A result’.
+  tests.atd = callTest tests/atd.nix {};
   tests.avahi = callTest tests/avahi.nix {};
   tests.bittorrent = callTest tests/bittorrent.nix {};
   tests.blivet = callTest tests/blivet.nix {};

nixos/tests/atd.nix

···
+import ./make-test.nix ({ pkgs, lib, ... }:
+
+{
+  name = "atd";
+  meta = with pkgs.stdenv.lib.maintainers; {
+    maintainers = [ bjornfor ];
+  };
+
+  machine =
+    { config, pkgs, ... }:
+    { services.atd.enable = true;
+      users.extraUsers.alice = { isNormalUser = true; };
+    };
+
+  # "at" has a resolution of 1 minute
+  testScript = ''
+    startAll;
+
+    $machine->fail("test -f ~root/at-1");
+    $machine->fail("test -f ~root/batch-1");
+    $machine->fail("test -f ~alice/at-1");
+    $machine->fail("test -f ~alice/batch-1");
+
+    $machine->succeed("echo 'touch ~root/at-1' | at now+1min");
+    $machine->succeed("echo 'touch ~root/batch-1' | batch");
+    $machine->succeed("su - alice -c \"echo 'touch at-1' | at now+1min\"");
+    $machine->succeed("su - alice -c \"echo 'touch batch-1' | batch\"");
+
+    $machine->succeed("sleep 1.5m");
+
+    $machine->succeed("test -f ~root/at-1");
+    $machine->succeed("test -f ~root/batch-1");
+    $machine->succeed("test -f ~alice/at-1");
+    $machine->succeed("test -f ~alice/batch-1");
+  '';
+})