public Set<Map.Entry<PropertyKey, Object>> entrySet() {
    return keySet().stream().map(key -> Maps.immutableEntry(key, get(key))).collect(toSet());
  }
@Test
  public void entrySet() {
    Set<Map.Entry<? extends PropertyKey, Object>> expected =
        PropertyKey.defaultKeys().stream()
            .map(key -> Maps.immutableEntry(key, key.getDefaultValue())).collect(toSet());
    assertThat(mProperties.entrySet(), is(expected));
    mProperties.put(mKeyWithValue, "value", Source.RUNTIME);
    expected.add(Maps.immutableEntry(mKeyWithValue, "value"));
    assertThat(mProperties.entrySet(), is(expected));
  }