@Test
  public void testConfig() {

    // tests around Config
    // set the custom props, then override with defaults
    System.setProperty("environment", "custom");

    final URL defaultPropsUrl = ConfigurationTest.class.getResource("/default.properties");
    Configuration.INSTANCE.addDefaultProperties(defaultPropsUrl, "default");

    // overridden
    Assert.assertThat(Configuration.INSTANCE.getString("overridden.key"), is("overridden"));

    // default
    Assert.assertThat(Configuration.INSTANCE.getString("default.key"), is("default-key"));

    // custom
    Assert.assertThat(Configuration.INSTANCE.getString("custom.key"), is("custom-key"));

    Assert.assertNull(Configuration.INSTANCE.getString("non-existant"));
  }