nix: introduce tests

Introduce set of tests based on NixOS test framework.

.github/workflows/build.yml

@@ -101,3 +101,20 @@ jobs:
       - name: Build yandex-music without flakes binaries
         run: nix build --impure .#yandex-music-noflakes
 
+  nix-test:
+    runs-on: ubuntu-latest
+    env:
+      NIXPKGS_ALLOW_UNFREE: 1
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          ref: ${{ (inputs.ref || '') }}
+
+      - name: Install nix
+        uses: cachix/install-nix-action@v22
+
+      - uses: DeterminateSystems/magic-nix-cache-action@v2
+
+      - name: Run NixOS tests
+        run: nix build --impure .#tests