nixos/tests: add simple dockerTools test

nixos/release.nix

···
   tests.containers-macvlans = callTest tests/containers-macvlans.nix {};
   tests.couchdb = callTest tests/couchdb.nix {};
   tests.docker = callTestOnTheseSystems ["x86_64-linux"] tests/docker.nix {};
+  tests.docker-tools = callTestOnTheseSystems ["x86_64-linux"] tests/docker-tools.nix {};
   tests.docker-edge = callTestOnTheseSystems ["x86_64-linux"] tests/docker-edge.nix {};
   tests.dovecot = callTest tests/dovecot.nix {};
   tests.dnscrypt-proxy = callTestOnTheseSystems ["x86_64-linux"] tests/dnscrypt-proxy.nix {};

nixos/tests/docker-tools.nix

···
+# this test creates a simple GNU image with docker tools and sees if it executes
+
+import ./make-test.nix ({ pkgs, ... }: {
+  name = "docker-tools";
+  meta = with pkgs.stdenv.lib.maintainers; {
+    maintainers = [ ];
+  };
+
+  nodes = {
+    docker =
+      { config, pkgs, ... }: {
+        virtualisation.docker.enable = true;
+      };
+  };
+
+  testScript =
+    let
+      dockerImage = pkgs.dockerTools.buildImage {
+        name = "hello-docker";
+        contents = [ pkgs.hello ];
+        tag = "sometag";
+
+        # TODO: create another test checking whether runAsRoot works as intended.
+
+        config = {
+          Cmd = [ "hello" ];
+        };
+      };
+
+    in ''
+      $docker->waitForUnit("sockets.target");
+      $docker->succeed("docker load --input='${dockerImage}'");
+      $docker->succeed("docker run hello-docker:sometag");
+    '';
+
+})