### Question:
HashBag implements MutableBag<T> { @Override public boolean removeOccurrence(T element) { return this.removeOccurrences(element, 1); }  @Override int sizeDistinct(); @Override int size(); @Override boolean isEmpty(); @Override boolean contains(Object o); @Override Object[] toArray(); void forEachWithIndex(BiConsumer<? super T, Integer> biConsumer); @Override T1[] toArray(T1[] array); @Override boolean add(T element); @Override boolean remove(Object o); @Override boolean containsAll(Collection<?> c); @Override boolean addAll(Collection<? extends T> c); @Override boolean removeAll(Collection<?> c); @Override boolean retainAll(Collection<?> c); @Override void clear(); @Override Iterator<T> iterator(); @Override int getOccurrences(T element); @Override boolean addOccurrence(T element); @Override boolean addOccurrences(T element, int occurrences); @Override boolean removeOccurrence(T element); @Override boolean removeOccurrences(T element, int occurrences); @Override void forEachWithOccurrences(BiConsumer<? super T, Integer> biConsumer); @Override void forEach(Consumer<? super T> consumer); @Override int hashCode(); @Override boolean equals(Object other);  }### Answer:
@Test public void removeOccurrence() { Assert.assertFalse(this.testObj.removeOccurrence("1")); Assert.assertEquals(MutableBag.empty(), this.testObj); this.testObj.withAll("1", "2", "3", "2", "3", "3"); Assert.assertTrue(this.testObj.removeOccurrence("1")); Assert.assertEquals(MutableBag.of("2", "2", "3", "3", "3"), this.testObj); Assert.assertTrue(this.testObj.removeOccurrence("2")); Assert.assertEquals(MutableBag.of("2", "3", "3", "3"), this.testObj); Assert.assertTrue(this.testObj.removeOccurrence("2")); Assert.assertEquals(MutableBag.of("3", "3", "3"), this.testObj); Assert.assertFalse(this.testObj.removeOccurrence("2")); }