add specs for global settings max age and asset serving response

spec/marten/conf/global_settings/assets_spec.cr

@@ -218,4 +218,19 @@ describe Marten::Conf::GlobalSettings::Assets do
       assets_conf.url.should eq "/assets/url/"
     end
   end
+
+  describe "#max_age" do
+    it "returns the expected default value" do
+      assets_conf = Marten::Conf::GlobalSettings::Assets.new
+      assets_conf.max_age.should eq 3600
+    end
+  end
+
+  describe "#max_age=" do
+    it "allows to set max_age value" do
+      assets_conf = Marten::Conf::GlobalSettings::Assets.new
+      assets_conf.max_age = 7200
+      assets_conf.max_age.should eq 7200
+    end
+  end
 end

spec/marten/middleware/asset_serving_spec.cr

@@ -255,7 +255,7 @@ describe Marten::Middleware::AssetServing do
       end
     end
 
-    it "properly sets the Cache-Control header" do
+    it "properly sets the default Cache-Control header" do
       middleware = Marten::Middleware::AssetServing.new
 
       ["BigApp.js", "css/BigApp.css"].each do |path|
@@ -280,5 +280,28 @@ describe Marten::Middleware::AssetServing do
         response.headers[:"Cache-Control"].should eq "private, max-age=3600"
       end
     end
+    it "properly sets the custom Cache-Control header" do
+      Marten.settings.assets.max_age = 7200
+      middleware = Marten::Middleware::AssetServing.new
+
+      ["BigApp.js", "css/BigApp.css"].each do |path|
+        response = middleware.call(
+          Marten::HTTP::Request.new(
+            ::HTTP::Request.new(
+              method: "GET",
+              resource: "/assets/#{path}",
+              headers: HTTP::Headers{
+                "Host"            => "example.com",
+                "Accept-Encoding" => "gzip, deflate, br",
+              }
+            )
+          ),
+          ->{ Marten::HTTP::Response.new("Unknown!", content_type: "text/plain", status: 200) }
+        )
+
+        uncompressed_content = File.read(File.join(__DIR__, "asset_serving/assets/#{path}"))
+        response.headers[:"Cache-Control"].should eq "private, max-age=7200"
+      end
+    end
   end
 end