### Question:
BinaryJoiningExpressionImpl implements JoiningExpression<T> { @Override public CharSequence separator() { return separator; } BinaryJoiningExpressionImpl(
            final CharSequence separator,
            final CharSequence prefix,
            final CharSequence suffix,
            final ToString<T> first,
            final ToString<T> second); @Override List<ToString<T>> expressions(); @Override CharSequence prefix(); @Override CharSequence suffix(); @Override CharSequence separator(); @Override String apply(T object);  }### Answer:
@Test void separator() { assertEquals(SEPARATOR, instance.separator()); }