alacritty: don't create file if settings is empty

Also add a few test cases for the alacritty module.

modules/programs/alacritty.nix

@@ -41,10 +41,13 @@ in
     };
   };
 
-  config = mkIf cfg.enable {
-    home.packages = [ pkgs.alacritty ];
+  config = mkMerge [
+    (mkIf cfg.enable {
+      home.packages = [ pkgs.alacritty ];
 
-    xdg.configFile."alacritty/alacritty.yml".text =
-      replaceStrings ["\\\\"] ["\\"] (builtins.toJSON cfg.settings);
-  };
+      xdg.configFile."alacritty/alacritty.yml" = mkIf (cfg.settings != {}) {
+        text = replaceStrings ["\\\\"] ["\\"] (builtins.toJSON cfg.settings);
+      };
+    })
+  ];
 }

tests/default.nix

@@ -36,6 +36,7 @@ import nmt {
   )
   // import ./modules/home-environment
   // import ./modules/misc/fontconfig
+  // import ./modules/programs/alacritty
   // import ./modules/programs/bash
   // import ./modules/programs/ssh
   // import ./modules/programs/tmux

tests/modules/programs/alacritty/default.nix

@@ -0,0 +1,4 @@
+{
+  alacritty-example-settings = ./example-settings.nix;
+  alacritty-empty-settings = ./empty-settings.nix;
+}

tests/modules/programs/alacritty/empty-settings.nix

@@ -0,0 +1,13 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+{
+  config = {
+    programs.alacritty.enable = true;
+
+    nmt.script = ''
+      assertPathNotExists home-files/.config/alacritty
+    '';
+  };
+}

tests/modules/programs/alacritty/example-settings-expected.yml

@@ -0,0 +1 @@
+{"key_bindings":[{"chars":"\x0c","key":"K","mods":"Control"}],"window":{"dimensions":{"columns":200,"lines":3}}}

tests/modules/programs/alacritty/example-settings.nix

@@ -0,0 +1,32 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+{
+  config = {
+    programs.alacritty = {
+      enable = true;
+
+      settings = {
+        window.dimensions = {
+          lines = 3;
+          columns = 200;
+        };
+
+        key_bindings = [
+          {
+            key = "K";
+            mods = "Control";
+            chars = "\\x0c";
+          }
+        ];
+      };
+    };
+
+    nmt.script = ''
+      assertFileContent \
+        home-files/.config/alacritty/alacritty.yml \
+        ${./example-settings-expected.yml}
+    '';
+  };
+}