Add test for `static#webapp_manifest`

spec/controllers/static_controller_spec.rb

@@ -38,4 +38,27 @@ describe StaticController, type: :controller do
       end
     end
   end
+
+  describe "#webapp_manifest" do
+    subject { get :webapp_manifest }
+
+    before do
+      stub_const("APP_CONFIG", {
+                   "site_name"      => "Specspring",
+                   "hostname"       => "test.host",
+                   "https"          => false,
+                   "items_per_page" => 5,
+                 })
+    end
+
+    it "returns a web app manifest" do
+      subject
+      expect(response).to have_http_status(200)
+      body = JSON.parse(response.body)
+
+      expect(body["name"]).to eq("Specspring")
+      expect(body["start_url"]).to eq("http://test.host/?source=pwa")
+      expect(body["scope"]).to eq("http://test.host/")
+    end
+  end
 end