### Question:
SingleElementList implements ICommonsList <ELEMENTTYPE> { @Nonnull public Object [] toArray () { if (m_bHasElement) { final Object [] aObjects = new Object [1]; aObjects[0] = m_aElement; return aObjects; } return ArrayHelper.EMPTY_OBJECT_ARRAY; } SingleElementList();  SingleElementList(@Nullable final ELEMENTTYPE aElement); @Override @Nonnull @ReturnsMutableCopy SingleElementList <T> createInstance(); @Nonnull @ReturnsMutableCopy SingleElementList <ELEMENTTYPE> getClone(); boolean add(@Nullable final ELEMENTTYPE aElement); void add(@Nonnegative final int nIndex, @Nullable final ELEMENTTYPE aElement); boolean addAll(@Nonnull final Collection <? extends ELEMENTTYPE> aElements); boolean addAll(@Nonnegative final int nIndex, @Nonnull final Collection <? extends ELEMENTTYPE> aElements); void clear(); boolean contains(@Nullable final Object aElement); boolean containsAll(@Nonnull final Collection <?> aElements); ELEMENTTYPE get(@Nonnegative final int nIndex); int indexOf(final Object aElement); boolean isEmpty(); @Nonnull Iterator <ELEMENTTYPE> iterator(); int lastIndexOf(@Nullable final Object aElement); @Nonnull ListIterator <ELEMENTTYPE> listIterator(); @Nonnull ListIterator <ELEMENTTYPE> listIterator(final int nIndex); @Nullable ELEMENTTYPE remove(final int nIndex); boolean remove(@Nullable final Object aElement); boolean removeAll(@Nullable final Collection <?> aElements); @UnsupportedOperation boolean retainAll(@Nonnull final Collection <?> aElements); @Nullable ELEMENTTYPE set(@Nonnegative final int nIndex, @Nullable final ELEMENTTYPE aNewElement); @Nonnegative int size(); @Nonnull @CodingStyleguideUnaware ICommonsList <ELEMENTTYPE> subList(@Nonnegative final int nFromIndex, @Nonnegative final int nToIndex); @Nonnull Object [] toArray(); @Nonnull ARRAYELEMENTTYPE [] toArray(@Nonnull final ARRAYELEMENTTYPE [] aDest); @Override boolean equals(final Object o); @Override int hashCode(); @Override String toString();  }### Answer:
@Test public void testStdMethods () { CommonsTestHelper.testDefaultImplementationWithEqualContentObject (new SingleElementList <> ("init"), new SingleElementList <> ("init")); CommonsTestHelper.testDefaultImplementationWithDifferentContentObject (new SingleElementList <> ("init"), new SingleElementList <> ("init2")); CommonsTestHelper.testDefaultImplementationWithDifferentContentObject (new SingleElementList <> ("init"), new SingleElementList <> (Boolean.TRUE)); assertArrayEquals (new SingleElementList <> ("init").toArray (), new SingleElementList <> ("init").toArray ()); assertArrayEquals (new SingleElementList <> ("init").toArray (new String [0]), new SingleElementList <> ("init").toArray (new String [0])); assertArrayEquals (new SingleElementList <> ("init").toArray (new String [1]), new SingleElementList <> ("init").toArray (new String [1])); assertArrayEquals (new SingleElementList <> ("init").toArray (new String [5]), new SingleElementList <> ("init").toArray (new String [5])); }