Quick Tip: Faking Dates in PHP with Carbon

Often there are scenarios where our code depends on the current time. Most programming languages handle datetime parsing pretty eloquently but a demand for simpler more humane date libraries have arisen. One of the best date libraries I've used is Carbon by Brian Nesbitt which could be briefly described as PHP's DateTime for humans. It's a must-to-have tool if you're developing anything complex with Laravel.

Suppose your project includes a routine that needs to save a new row to database but only on specified working days (no weekends, no public holidays). It's trivial to implement date validation by calling, for example, Carbon::today() which returns a new object representing the current day.

For asserting that your logic works as intended you would write unit tests as usual. However, you might end up in a situation where your unit tests would fail if the current day is a non-working day. Next, imagine you're practicing continous delivery – like you probably should – and you can't deploy a critical fix to production until tomorrow because of a failing pipeline. How would you explain this to the client? You would probably just mark this test as incomplete so the entire pipeline could pass even if a single unit test would fail.

Fortunately, Carbon offers a simple solution for faking dates in unit tests. You only need to mock the current date to a given Carbon instance with setTestNow() method like so:

// Set test date to 12:00 on 18th June, 2018
$testDate = Carbon::create(2018, 6, 18, 12);
Carbon::setTestNow($testDate);

// Execute the logic
BusinessClass::doStuff();

// Check the results
$this->assertDatabaseHas('stuff', [
    // The data you need...
]);

// IMPORTANT: Reset the date to not affect the next test!
Carbon::setTestNow();

As you can see, faking dates in tests is very easy. Just don't forget to reset the date or you might experience more failing tests.