@Test public void testRemove() throws Exception {

  // given
  String givenKey = GIVEN_KEY;
  prefser.put(givenKey, 1);
  // when
  assertThat(prefser.contains(givenKey)).isTrue();
  prefser.remove(givenKey);
  // then
  assertThat(prefser.contains(givenKey)).isFalse();
}