### Question:
PatternBlock implements Block { @Override public BooleanExpression exists() { return BooleanOperation.create(Ops.EXISTS, Blocks.group(this)); } PatternBlock(Expression<ID> subject, Expression<UID> predicate, Expression<NODE> object, @Nullable Expression<UID> context);  PatternBlock(Expression<ID> subject, Expression<UID> predicate, Expression<NODE> object); OptionalBlock asOptional(); Expression<ID> getSubject(); Expression<UID> getPredicate(); Expression<NODE> getObject(); @Nullable Expression<UID> getContext(); @Override Predicate not(); @Override @SuppressWarnings("unchecked") R accept(Visitor<R, C> v, C context); @Override Class<? extends Boolean> getType(); @Override BooleanExpression exists(); @Override int hashCode(); @Override boolean equals(Object o); @Override String toString();  }### Answer:
@Test public void Exists() { assertEquals("exists { {s} {p} {o} . }", Blocks.SPO.exists().toString()); }