nix: introduce tests

Introduce set of tests based on NixOS test framework.

nix/module.nix

@@ -1,6 +1,7 @@
 {
   yandex-music-with,
   isHm ? false,
+  isTest ? false,
 }:
 {
   lib,
@@ -13,14 +14,18 @@ let
 
 in
 {
+  /*
+    The NixOS test framework disallow to extend `nixpkgs.overlays` configuration
+    option, so we make it here conditionally.
+  */
   imports = [
-    {
+    (lib.mkIf (!isTest) {
       nixpkgs.overlays = [
         (final: prev: {
           yandex-music = yandex-music-with prev;
         })
       ];
-    }
+    })
   ];
 
   options = {

nix/test-suite.nix

@@ -0,0 +1,62 @@
+/*
+  This test suite uses nixos common x11 and user-account test configurations.
+  Those configurations use auto-login to ice-wm desktop manager.
+  This test configuration enables yandex-music application, launches it and
+  check for window existence. Additionally it takes screenshot after successful
+  launch to allow to validate state manually. The result may miss the content
+  inside window because of lack of GPU support.
+
+  TODO(Shvedov): We should to perform automatic checks of screen state.
+*/
+{
+  testers,
+  path,
+
+  # The yandex-music module
+  nixosModule,
+  # The extra configuration
+  configuration ? { },
+  # The extra code of test script
+  extraTestScript ? "",
+  # The name of test
+  name ? "yandex-music-test",
+}:
+testers.runNixOSTest {
+  inherit name;
+  nodes.machine =
+    let
+      tests = "${path}/nixos/tests/common/";
+      user = "alice";
+    in
+    {
+      imports = [
+        nixosModule
+        "${tests}/x11.nix"
+        "${tests}/user-account.nix"
+        configuration
+      ];
+      test-support.displayManager.auto.user = user;
+      programs.yandex-music.enable = true;
+    };
+
+  testScript =
+    ''
+      # We have to execute command with su beckause all commands performs under
+      # the root user.
+      def mk_command(command, tail = "", fork = False):
+        if fork:
+          tail = f"{tail} >&2 &"
+        return f"su -c '{command}' - alice {tail}"
+
+      machine.wait_for_x()
+      machine.execute(mk_command("yandex-music", fork = True))
+
+      check_command = mk_command('xwininfo -root -tree', tail = "| grep 'Яндекс Музыка'")
+
+      machine.wait_until_succeeds(check_command, 120)
+      machine.sleep(40)
+      machine.succeed(check_command)
+      machine.screenshot("screen")
+    ''
+    + extraTestScript;
+}

nix/test.nix

@@ -0,0 +1,81 @@
+/*
+  This is set of tests of yandex-music application. The main purpose of this
+  test is to check the NixOS module for yandex-music and whether its runs
+  successfully with such configuration.
+*/
+{
+  pkgs,
+  yandex-music-with,
+  nixosModule,
+  linkFarm,
+  lib,
+}:
+let
+  # Extend packages with our package to overcome the limitation of nixOSTest
+  # modules regarding the overlays.
+  pkgs' = pkgs.extend (cur: prev: { yandex-music = yandex-music-with prev; });
+  removeNameAttr = attrs: lib.removeAttrs attrs [ "name" ];
+  test-suite =
+    {
+      name ? "yandex-music-test",
+      ...
+    }@configuration:
+    pkgs'.callPackage ./test-suite.nix {
+      inherit nixosModule name;
+      configuration = removeNameAttr configuration;
+    };
+  yandex-music-config = cfg: {
+    programs.yandex-music = cfg;
+  };
+  yandex-music-test-suite =
+    {
+      name,
+      ...
+    }@cfg:
+    test-suite (
+      (yandex-music-config (removeNameAttr cfg))
+      // {
+        name = "yandex-music-test-${name}";
+      }
+    );
+  /*
+    This is set of similar tests with slightly different configuration options
+    for yandex-music module. All they will be joined together to package with
+    symlinks to all results.
+  */
+  tests = {
+    base = test-suite { };
+    trayDefault = yandex-music-test-suite {
+      tray.enable = true;
+      name = "tray-default";
+    };
+    trayAlways = yandex-music-test-suite {
+      tray.enable = true;
+      tray.always = true;
+      name = "tray-always";
+    };
+    trayMonoBlack = yandex-music-test-suite {
+      tray.enable = true;
+      tray.style = 2;
+      name = "tray-mono-black";
+    };
+    trayMonoWhite = yandex-music-test-suite {
+      tray.enable = true;
+      tray.style = 3;
+      name = "tray-mono-white";
+    };
+    devTools = yandex-music-test-suite {
+      devTools.enable = true;
+      name = "dev-tools";
+    };
+    customTitleBar = yandex-music-test-suite {
+      customTitleBar.enable = true;
+      name = "custom-title-bar";
+    };
+    animatiosFpsZero = yandex-music-test-suite {
+      vibeAnimationMaxFps = 0;
+      name = "animation-fps-zero";
+    };
+  };
+in
+(linkFarm "yandex-music-test-all" tests) // tests