aria2: add systemd service

tests/modules/programs/aria2/default.nix

@@ -1,4 +1,8 @@
+{ lib, pkgs, ... }:
 {
   aria2-disabled = ./disabled.nix;
   aria2-settings = ./settings.nix;
 }
+// lib.optionalAttrs pkgs.stdenv.hostPlatform.isLinux {
+  aria2-systemd = ./systemd.nix;
+}

tests/modules/programs/aria2/systemd.nix

@@ -0,0 +1,25 @@
+{ config, ... }:
+{
+  programs.aria2 = {
+    enable = true;
+    package = config.lib.test.mkStubPackage { outPath = "@aria2@"; };
+    systemd.enable = true;
+  };
+
+  nmt.script = ''
+    assertFileContent \
+      home-files/.config/systemd/user/aria2.service \
+      ${builtins.toFile "aria2.service" ''
+        [Install]
+        WantedBy=default.target
+
+        [Service]
+        ExecStart=@aria2@/bin/dummy --enable-rpc
+        Restart=on-failure
+
+        [Unit]
+        Description=Aria2c daemon
+        Documentation=man:aria2c(1)
+      ''}
+  '';
+}