Checks to see whether a block does not appears on the page.
\Drupal\block\Plugin\Core\Entity\Block $block: The block entity to find on the page.
protected function assertNoBlockAppears(Block $block) {
$result = $this
->findBlockInstance($block);
$this
->assertFalse(!empty($result), format_string('Ensure the block @id does not appear on the page', array(
'@id' => $block
->id(),
)));
}