@Test
 public void properSubsetNotEmpty() {
   MutableSet<String> singletonSet = UnifiedSet.newSetWith("Bertha");
   MutableSet<String> doubletonSet = UnifiedSet.newSetWith("Bertha", "Myra");
   Assert.assertTrue(Sets.isProperSubsetOf(singletonSet, doubletonSet));
   Assert.assertFalse(Sets.isProperSubsetOf(doubletonSet, singletonSet));
 }
 @Test
 public void properSubsetEqual() {
   MutableSet<String> setA = UnifiedSet.newSetWith("Bertha", null, "Myra");
   MutableSet<String> setB = UnifiedSet.newSetWith("Myra", "Bertha", null);
   Assert.assertFalse(Sets.isProperSubsetOf(setA, setB));
   Assert.assertFalse(Sets.isProperSubsetOf(setB, setA));
 }
 @Test
 public void properSubsetEmpty() {
   MutableSet<String> emptySet = mSet();
   MutableSet<String> singletonSet = UnifiedSet.newSetWith("Bertha");
   Assert.assertTrue(Sets.isProperSubsetOf(emptySet, singletonSet));
   Assert.assertFalse(Sets.isProperSubsetOf(singletonSet, emptySet));
 }