public function test_action_callback_manipulation_while_running() {
    $tag = __FUNCTION__;
    $a   = new MockAction();
    $b   = new MockAction();
    $c   = new MockAction();
    $d   = new MockAction();
    $e   = new MockAction();

    add_action( $tag, array( $a, 'action' ), 11, 2 );
    add_action( $tag, array( $this, 'action_that_manipulates_a_running_hook' ), 12, 2 );
    add_action( $tag, array( $b, 'action' ), 12, 2 );

    do_action( $tag, $tag, array( $a, $b, $c, $d, $e ) );
    do_action( $tag, $tag, array( $a, $b, $c, $d, $e ) );

    $this->assertSame( 2, $a->get_call_count(), 'callbacks should run unless otherwise instructed' );
    $this->assertSame( 1, $b->get_call_count(), 'callback removed by same priority callback should still get called' );
    $this->assertSame( 1, $c->get_call_count(), 'callback added by same priority callback should not get called' );
    $this->assertSame( 2, $d->get_call_count(), 'callback added by earlier priority callback should get called' );
    $this->assertSame( 1, $e->get_call_count(), 'callback added by later priority callback should not get called' );
  }