TDDing with function-mocker

Where I start TDDing a small WordPress component using function-mocker.

The idea

I’m trying to create a re-usable component capable of abstracting the operations needed to schedule an action using WordPress Cron functions into a re-usable plug-and-play object.
Right now I will write the smallest possible piece of code strict TDD allows writing without writing a test first: the interface the class will expose.

The interface

Pretty much self-explanatory in its methods the idea is to lay down “the final result” any other component will interact with:

namespace Schedule;

use Schedule\Activation_Time\Activation_Time_Interface;
use Schedule\Recurrence_Interval\Recurrence_Interval_Interface;

interface Schedule {

    /**
     * Checks if an hook is scheduled or not.
     *
     * @param       $hook
     * @param array $args
     *
     * @return bool
     */
    public function is_scheduled( $hook, array $args = null );

    /**
     * Schedules an event.
     *
     * @param                               $hook
     * @param Activation_Time_Interface     $activation_time
     * @param Recurrence_Interval_Interface $recurrence_interval
     * @param array                         $args
     *
     * @return mixed
     */
    public function schedule( $hook, Activation_Time_Interface $activation_time, Recurrence_Interval_Interface $recurrence_interval, array $args = null );

    /**
     * Removes an event from the schedule.
     *
     * @param       $hook
     * @param array $args
     *
     * @return mixed
     */
    public function clear_schedule( $hook, array $args = null );

    /**
     * Schedules a single event.
     *
     * @param                           $hook
     * @param Activation_Time_Interface $activation_Time
     * @param array                     $args
     *
     * @return mixed
     */
    public function schedule_single_event( $hook, Activation_Time_Interface $activation_Time, array $args = null );

    /**
     * Updates the schedule for an event.
     *
     * @param                               $hook
     * @param Activation_Time_Interface     $activation_Time
     * @param Recurrence_Interval_Interface $recurrence_Interval
     * @param array                         $args
     *
     * @return mixed
     */
    public function reschedule( $hook, Activation_Time_Interface $activation_Time, Recurrence_Interval_Interface $recurrence_Interval, array $args = null );
}

The idea is not to make anything revolutionary but to develop a TDD WordPress component using the function replacement possibility function-mocker offers and test the tool in the process.

I appreciate your input