add nixos test fro build-on-remote

tests/flake-module.nix

@@ -18,5 +18,7 @@
       from-nixos-stable = import ./from-nixos.nix testInputsStable;
       from-nixos-with-sudo = import ./from-nixos-with-sudo.nix testInputsUnstable;
       from-nixos-with-sudo-stable = import ./from-nixos-with-sudo.nix testInputsStable;
+
+      from-nixos-build-on-remote = import ./from-nixos-build-on-remote.nix testInputsUnstable;
     });
 }

tests/from-nixos-build-on-remote.nix

@@ -0,0 +1,43 @@
+(import ./lib/test-base.nix) {
+  name = "from-nixos-build-on-remote";
+  nodes = {
+    installer = ./modules/installer.nix;
+    installed = {
+      services.openssh.enable = true;
+      virtualisation.memorySize = 1512;
+
+      users.users.root.openssh.authorizedKeys.keyFiles = [ ./modules/ssh-keys/ssh.pub ];
+    };
+  };
+  testScript = ''
+    def create_test_machine(oldmachine=None, args={}): # taken from <nixpkgs/nixos/tests/installer.nix>
+        machine = create_machine({
+          "qemuFlags":
+            '-cpu max -m 1024 -virtfs local,path=/nix/store,security_model=none,mount_tag=nix-store,'
+            f' -drive file={oldmachine.state_dir}/installed.qcow2,id=drive1,if=none,index=1,werror=report'
+            f' -device virtio-blk-pci,drive=drive1',
+        } | args)
+        driver.machines.append(machine)
+        return machine
+    start_all()
+
+    installer.succeed("""
+      nixos-anywhere \
+        -i /root/.ssh/install_key \
+        --debug \
+        --build-on-remote \
+        --kexec /etc/nixos-anywhere/kexec-installer \
+        --store-paths /etc/nixos-anywhere/disko /etc/nixos-anywhere/system-to-install \
+        root@installed >&2
+    """)
+    try:
+      installed.shutdown()
+    except BrokenPipeError:
+      # qemu has already exited
+      pass
+    new_machine = create_test_machine(oldmachine=installed, args={ "name": "after_install" })
+    new_machine.start()
+    hostname = new_machine.succeed("hostname").strip()
+    assert "nixos-anywhere" == hostname, f"'nixos-anywhere' != '{hostname}'"
+  '';
+}