Conditionally Assert Throwing An Exception In Pest

Pest recently added the throwsUnless() method in Pest v2.24 to conditionally verify an exception if a given boolean expression evaluates to false.

This method is the counterpart to the throwIf() method, which conditionally verifies an exception if a given expression is true:

test('example 1', function () {
    // Test that only throws an exception for the mysql driver...
})->throwsIf(DB::getDriverName() === 'mysql', Exception::class, 'MySQL is not supported.');

test('example 2', function () {
    // Test that throws unless the db driver is mysql...
})->throwsUnless(DB::getDriverName() === 'mysql', SomeDBException::class);

For example, let's say that you have a PHP package that supports various PHP extensions for manipulating images. Your CI environment might support and test both gd and imagemagick; however, other environments might only support one or the other:

test('gd wrapper can create an image', function () {
    $image = imagecreate(width: 200, height: 200);
    imagecolorallocate($image, 255, 255, 255);
    imagepng($image, '/tmp/new_image_gd.png');

    expect(file_exists('/tmp/new_image_gd.png'))->toBeTrue();
})->throwsUnless(extension_loaded('gd'), \Error::class);

test('imagemagic wrapper can create an image', function () {
    $image = new Imagick();
    // ...

})->throwsUnless(extension_loaded('imagick'), \Error::class);

The throwsIf() and throwsUnless() methods also support callables if you prefer that style or have some custom logic that you want to use to determine if the test should throw an exception:

test('example test with callables', function () {
    $image = new Imagick();
    // ...
})->throwsUnless(fn () => class_exists(\Imagick::class), 'Class "Imagick" not found');

Learn More

You can learn about handling Exceptions in tests in the Pest Exceptions documentation. Also, if you're new to PestPHP and prefer videos, we recommend checking out Learn PestPHP From Scratch by Luke Downing.