### Question:
SpaceBlock extends AbstractBlock { @Override public boolean equals(Object obj) { return obj instanceof SpaceBlock && super.equals(obj); }  @Override void traverse(Listener listener); @Override String toString(); @Override boolean equals(Object obj); @Override int hashCode();  }### Answer:
@Test public void testEquals() { assertEquals(new SpaceBlock(), new SpaceBlock()); assertNotEquals(new SpaceBlock(), new WordBlock("toto")); assertNotEquals(new WordBlock("toto"), new SpaceBlock()); }