### Question:
GroupBlock implements ContainerBlock { @Override public BooleanExpression exists() { return BooleanOperation.create(Ops.EXISTS, this); } GroupBlock(List<Block> blocks, Predicate... filters); @Override Predicate not(); @Override @SuppressWarnings("unchecked") R accept(Visitor<R, C> v, C context); @Override Class<? extends Boolean> getType(); List<Block> getBlocks(); @Nullable Predicate getFilters(); @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.group(Blocks.SPO).exists().toString()); }