nix: introduce tests

Introduce set of tests based on NixOS test framework.

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