nixos-test: use evaluated kexec image

flake.nix

@@ -4,8 +4,10 @@
   inputs.nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
   inputs.disko.url = "github:nix-community/disko/master";
   inputs.disko.inputs.nixpkgs.follows = "nixpkgs";
+  # used for testing
+  inputs.nixos-images.url = "github:nix-community/nixos-images";
 
-  outputs = { self, disko, nixpkgs, ... }:
+  outputs = { self, disko, nixpkgs, nixos-images, ... }:
     let
       supportedSystems = [
         "x86_64-linux"
@@ -32,6 +34,7 @@
           from-nixos = import ./tests/from-nixos.nix {
             inherit pkgs;
             disko = disko.nixosModules.disko;
+            kexec-installer = nixos-images.packages.${pkgs.system}.kexec-installer-nixos-unstable;
             makeTest = import (pkgs.path + "/nixos/tests/make-test-python.nix");
             eval-config = import (pkgs.path + "/nixos/lib/eval-config.nix");
           };

tests/from-nixos.nix

@@ -2,12 +2,9 @@
 , makeTest ? import <nixpkgs/nixos/tests/make-test-python.nix>
 , eval-config ? import <nixpkgs/nixos/lib/eval-config.nix>
 , disko ? "${builtins.fetchTarball "https://github.com/nix-community/disko/archive/master.tar.gz"}/module.nix"
+, kexec-installer
 , ... }:
 let
-  kexec_tarball = builtins.fetchurl {
-    url = "https://github.com/nix-community/nixos-images/releases/download/nixos-22.05/nixos-kexec-installer-x86_64-linux.tar.gz";
-    sha256 = "sha256:1ff7rc0n8w1vab7k9sir3029sizfaq8yx7y8r1id94gcqrr2n1sd";
-  };
   systemToInstall = { modulesPath, ... }: {
     imports = [
       disko
@@ -114,7 +111,7 @@ makeTest {
       ssh-add /etc/sshKey
       ${../nixos-remote} \
         --no-ssh-copy-id \
-        --kexec ${kexec_tarball} \
+        --kexec ${kexec-installer}/nixos-kexec-installer-${pkgs.stdenv.hostPlatform.system}.tar.gz \
         --store-paths ${toString evaledSystem.config.system.build.disko} ${toString evaledSystem.config.system.build.toplevel} \
         root@installed >&2
     """)