public function test_has_filter_after_remove_all_filters() {
    $a   = new MockAction();
    $tag = __FUNCTION__;
    $val = __FUNCTION__ . '_val';

    // No priority.
    add_filter( $tag, array( $a, 'filter' ), 11 );
    add_filter( $tag, array( $a, 'filter' ), 12 );
    $this->assertTrue( has_filter( $tag ) );

    remove_all_filters( $tag );
    $this->assertFalse( has_filter( $tag ) );

    // Remove priorities one at a time.
    add_filter( $tag, array( $a, 'filter' ), 11 );
    add_filter( $tag, array( $a, 'filter' ), 12 );
    $this->assertTrue( has_filter( $tag ) );

    remove_all_filters( $tag, 11 );
    remove_all_filters( $tag, 12 );
    $this->assertFalse( has_filter( $tag ) );
  }