public function logout()
	{
		if ( ! $this->is_logged_in() ) {
			return false; // user isn't login.
		}

		$page = $this->getSession()->getPage();
		$logout = $page->find( "css", "#wp-admin-bar-logout a" );

		if ( ! empty( $logout ) ) {
			$this->getSession()->visit( $this->locatePath( $logout->getAttribute( "href" ) ) );

			for ( $i = 0; $i < $this->timeout; $i++ ) {
				try {
					$url = $this->getSession()->getCurrentUrl();
					if ( strpos( $url, "loggedout=true" ) ) {
						return true;
					}
				} catch ( \Exception $e ) {
					// do nothing
				}

				sleep( 1 );
			}

			throw new \Exception( 'Logout timeout' );
		}
	}