avizo: don't write a config file if settings are empty

Before this change, the default config provided by this module wrote
an empty file to `$HOME/.config/avizo/config.ini`, which caused a
bunch of errors, as Avizo tries to read a 'group' from the ini file,
which fails.

This commit also adds associated test cases.

PR #3871

modules/services/avizo.nix

@@ -47,10 +47,11 @@ in {
     assertions =
       [ (hm.assertions.assertPlatform "services.avizo" pkgs platforms.linux) ];
 
-    home.packages = [ cfg.package ];
+    xdg.configFile."avizo/config.ini" = mkIf (cfg.settings != { }) {
+      source = settingsFormat.generate "avizo-config.ini" cfg.settings;
+    };
 
-    xdg.configFile."avizo/config.ini".source =
-      settingsFormat.generate "avizo-config.ini" cfg.settings;
+    home.packages = [ cfg.package ];
 
     systemd.user = {
       services.avizo = {

tests/default.nix

@@ -169,6 +169,7 @@ import nmt {
     ./modules/programs/wlogout
     ./modules/programs/xmobar
     ./modules/programs/yt-dlp
+    ./modules/services/avizo
     ./modules/services/barrier
     ./modules/services/borgmatic
     ./modules/services/cachix-agent

tests/modules/services/avizo/default.nix

@@ -0,0 +1,4 @@
+{
+  avizo-with-settings = ./with-settings.nix;
+  avizo-without-settings = ./without-settings.nix;
+}

tests/modules/services/avizo/with-settings.nix

@@ -0,0 +1,54 @@
+{ ... }:
+
+{
+  services.avizo = {
+    enable = true;
+    settings = {
+      default = {
+        time = 1.0;
+        y-offset = 0.5;
+        fade-in = 0.1;
+        fade-out = 0.2;
+        padding = 10;
+      };
+    };
+  };
+
+  test.stubs.avizo = { };
+
+  nmt.script = ''
+    serviceFile=home-files/.config/systemd/user/avizo.service
+    assertFileExists $serviceFile
+    assertFileContent $serviceFile ${
+      builtins.toFile "expected" ''
+        [Install]
+        WantedBy=graphical-session.target
+
+        [Service]
+        ExecStart=@avizo@/bin/avizo-service
+        Restart=always
+        Type=simple
+
+        [Unit]
+        After=graphical-session.target
+        ConditionEnvironment=WAYLAND_DISPLAY
+        Description=Volume/backlight OSD indicator
+        Documentation=man:avizo(1)
+        PartOf=graphical-session.target
+      ''
+    }
+
+    configFile=home-files/.config/avizo/config.ini
+    assertFileExists $configFile
+    assertFileContent $configFile ${
+      builtins.toFile "expected" ''
+        [default]
+        fade-in=0.100000
+        fade-out=0.200000
+        padding=10
+        time=1.000000
+        y-offset=0.500000
+      ''
+    }
+  '';
+}

tests/modules/services/avizo/without-settings.nix

@@ -0,0 +1,33 @@
+{ ... }:
+
+{
+  services.avizo.enable = true;
+
+  test.stubs.avizo = { };
+
+  nmt.script = ''
+    serviceFile=home-files/.config/systemd/user/avizo.service
+    assertFileExists $serviceFile
+    assertFileContent $serviceFile ${
+      builtins.toFile "expected" ''
+        [Install]
+        WantedBy=graphical-session.target
+
+        [Service]
+        ExecStart=@avizo@/bin/avizo-service
+        Restart=always
+        Type=simple
+
+        [Unit]
+        After=graphical-session.target
+        ConditionEnvironment=WAYLAND_DISPLAY
+        Description=Volume/backlight OSD indicator
+        Documentation=man:avizo(1)
+        PartOf=graphical-session.target
+      ''
+    }
+
+    configFile=home-files/.config/avizo/config.ini
+    assertPathNotExists $configFile
+  '';
+}