Ultra-simple clock abstraction for PHP 7, allowing developers to properly mock time-related functions

v1.1 2016-08-29 01:20 UTC


You can use this library to help unit test applications that have a reliance on the clock in some way.


Unit tests are better when they are completely isolated from the environment in which they are run, and don't ever access parts of that environment such as databases, file system, network sockets or even the current time. I have come across multiple examples of unit tests whose results changed based on when you run them, because they rely on the PHP time functions and behaviour changes as a result.

It's important to be able to test some classes with different time or date related inputs being used to test different aspects. Some libraries exist that let you change the results of the built in time functions by calling some code, but to me the solution is much simpler - you should isolate your code from the clock by injecting it into the class instead, therefore allowing you to mock the results using your favourite unit testing framework.

Libraries that I have found so far using this either come as part of a much bigger library that I didn't require all the complexity of, or didn't have a stable release tagged, or had other issues, so I created this library to use instead. I would often create a similar interface in applications and thought I may as well make it a reusable component.

It is deliberately ultra-simple, with no frills, containing just enough to achieve the required results without any added complexity.


Clock requires PHP 7. Install via composer:

composer require cemerson/clock


Whenever you have a class that needs to reference the current time, don't call any time related functions in PHP. Instead, hint for and inject the Clock interface from this library.

In production, you can set up your dependency injection container to inject the provided Wallclock class to obtain the current time. This class takes a DateTimeZone object in the constructor and provides a DateTimeImmutable object with the current time, using the time zone provided when its getDateTime() method is called.

<?php declare(strict_types = 1);

namespace MyVendor\MyApp;

use CEmerson\Clock;

class MyClass
    /** @var Clock */
    private $clock;
    public function __construct(Clock $clock)
        $this->clock = $clock;
    public function myMethodThatNeedsCurrentTime()
        $currentDateTime = $this->clock->getDateTime();
        /* ... */

Alternatively, create your own implementation of the Clock interface if you need some different functionality, or you need the mutable version of the DateTimeInterface instead.

During testing, you can create a mock of the Clock interface to provide whatever time/date combination you like using your favourite mocking framework, or even using your least favourite one.