adds spec for Setting

spec/models/setting_spec.rb

@@ -0,0 +1,15 @@
+require 'rails_helper'
+
+describe Setting do
+
+  it "should be accesible by key" do
+    create(:setting, key: "Important Setting", value: "42")
+
+    expect(Setting.value_for("Important Setting")).to eq("42")
+  end
+
+  it "should be nil if key does not exist" do
+    expect(Setting.value_for("Undefined key")).to be_nil
+  end
+
+end