spatie/phpunit-snapshot-assertions

1.2.0 2017-11-29 22:08 UTC

README

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Snapshot testing is a way to test without writing actual test cases

use Spatie\Snapshots\MatchesSnapshots;

class OrderTest
{
    use MatchesSnapshot;

    class test_it_casts_to_json()
    {
        $order = new Order(1);

        $this->assertMatchesJsonSnapshot($order->toJson());
    }
}

On the first run, the test runner will create a new snapshot.

> ./vendor/bin/phpunit

There was 1 incomplete test:

1) OrderTest::test_it_casts_to_json
Snapshot created for OrderTest__test_it_casts_to_json__1

OK, but incomplete, skipped, or risky tests!
Tests: 1, Assertions: 0, Incomplete: 1.

On subsequent runs, the test will pass as long as the snapshot doesn't change.

> ./vendor/bin/phpunit

OK (1 test, 1 assertion)

If there's a regression, the test will fail!

$orderId = new Order(2); // Regression! Was `1`
> ./vendor/bin/phpunit

1) OrderTest::test_it_casts_to_json
Failed asserting that two strings are equal.
--- Expected
+++ Actual
@@ @@
Failed asserting that '{"id":2}' matches JSON string "{
    "id": 1
}

FAILURES!
Tests: 1, Assertions: 1, Failures: 1.

Installation

You can install the package via composer:

composer require spatie/phpunit-snapshot-assertions

Usage

To make snapshot assertions, use the Spatie\Snapshots\MatchesSnapshots trait in your test case class. This adds five assertion methods to the class:

  • assertMatchesSnapshot($actual)
  • assertMatchesJsonSnapshot($actual)
  • assertMatchesXmlSnapshot($actual)
  • assertMatchesFileSnapshot($filePath)
  • assertMatchesFileHashSnapshot($filePath)

Snapshot Testing 101

Let's do a snapshot assertion for a simple string, "foo".

public function test_it_is_foo() {
    $this->assertMatchesSnapshot('foo');
}

The first time the assertion runs, it doesn't have a snapshot to compare the string with. The test runner generates a new snapshot and marks the test as incomplete.

> ./vendor/bin/phpunit

There was 1 incomplete test:

1) ExampleTest::test_it_matches_a_string
Snapshot created for ExampleTest__test_it_matches_a_string__1

OK, but incomplete, skipped, or risky tests!
Tests: 1, Assertions: 0, Incomplete: 1.

Snapshot ids are generated based on the test and testcase's names. Basic snapshots return a var_export of the actual value.

<?php return 'foo';

Let's rerun the test. The test runner will see that there's already a snapshot for the assertion and do a comparison.

> ./vendor/bin/phpunit

OK (1 test, 1 assertion)

If we change actual value to "bar", the test will fail because the snapshot still returns "foo".

public function test_it_is_foo() {
    $this->assertMatchesSnapshot('bar');
}
> ./vendor/bin/phpunit

1) ExampleTest::test_it_matches_a_string
Failed asserting that two strings are equal.
--- Expected
+++ Actual
@@ @@
-'foo'
+'bar'

FAILURES!
Tests: 1, Assertions: 1, Failures: 1.

When we expect a changed value, we need to tell the test runner to update the existing snapshots instead of failing the test. This is possible by adding a-d --update-snapshots flag to the phpunit command.

> ./vendor/bin/phpunit -d --update-snapshots

OK (1 test, 1 assertion)

As a result, our snapshot file returns "bar" instead of "foo".

<?php return 'bar';

File snapshots

The MatchesSnapshots trait offers two ways to assert that a file is identical to the snapshot that was made the first time the test was run:

The assertMatchesFileHashSnapshot($filePath) assertion asserts that the hash of the file passed into the function and the hash saved in the snapshot match. This assertion is fast and uses very little disk space. The downside of this assertion is that there is no easy way to see how the two files differ if the test fails.

The assertMatchesFileSnapshot($filePath) assertion works almost the same way as the file hash assertion, except that it actually saves the whole file in the snapshots directory. If the assertion fails, it places the failed file next to the snapshot file so they can easily be manually compared. The persisted failed file is automatically deleted when the test passes. This assertion is most useful when working with binary files that should be manually compared like images or pdfs.

Customizing Snapshot Ids and Directories

Snapshot ids are generated via the getSnapshotId method on the MatchesSnapshot trait. Override the method to customize the id. By default, a snapshot id exists of the test name, the test case name and an incrementing value, e.g. Test__my_test_case__1.

Example: Replacing the __ Delimiter With --

protected function getSnapshotId(): string
{
    return (new ReflectionClass($this))->getShortName().'--'.
        $this->getName().'--'.
        $this->snapshotIncrementor;
}

By default, snapshots are stored in a __snapshots__ directory relative to the test class. This can be changed by overriding the getSnapshotDirectory method.

Example: Renaming the __snapshots__ directory to snapshots

protected function getSnapshotDirectory(): string
{
    return dirname((new ReflectionClass($this))->getFileName()).
        DIRECTORY_SEPARATOR.
        'snapshots';
}

Writing Custom Drivers

Drivers ensure that different types of data can be serialized and matched in their own way. A driver is a class that implements the Spatie\Snapshots\Driver interface, which requires three method implementations: serialize, extension and match.

Let's take a quick quick look at the JsonDriver.

namespace Spatie\Snapshots\Drivers;

use PHPUnit\Framework\Assert;
use Spatie\Snapshots\Driver;
use Spatie\Snapshots\Exceptions\CantBeSerialized;

class JsonDriver implements Driver
{
    public function serialize($data): string
    {
        if (! is_string($data)) {
            throw new CantBeSerialized('Only strings can be serialized to json');
        }

        return json_encode(json_decode($data), JSON_PRETTY_PRINT).PHP_EOL;
    }

    public function extension(): string
    {
        return 'json';
    }

    public function match($expected, $actual)
    {
        Assert::assertJsonStringEqualsJsonString($actual, $expected);
    }
}
  • The serialize method returns a string which will be written to the snapshot file. In the JsonDriver, we'll decode and re-encode the json string to ensure the snapshot has pretty printing.
  • We want to save json snapshots as json files, so we'll use json as their file extension.
  • When matching the expected data with the actual data, we want to use PHPUnit's built in json assertions, so we'll call the specific assertJsonStringEqualsJsonString method.

Drivers can be used by passing them as assertMatchesSnapshot's second argument.

$this->assertMatchesSnapshot($something->toYaml(), new MyYamlDriver());

Changelog

Please see CHANGELOG for more information what has changed recently.

Testing

composer test

Contributing

Please see CONTRIBUTING for details.

Security

If you discover any security related issues, please email freek@spatie.be instead of using the issue tracker.

Postcardware

You're free to use this package, but if it makes it to your production environment we highly appreciate you sending us a postcard from your hometown, mentioning which of our package(s) you are using.

Our address is: Spatie, Samberstraat 69D, 2060 Antwerp, Belgium.

We publish all received postcards on our company website.

Credits

Support us

Spatie is a webdesign agency based in Antwerp, Belgium. You'll find an overview of all our open source projects on our website.

Does your business depend on our contributions? Reach out and support us on Patreon. All pledges will be dedicated to allocating workforce on maintenance and new awesome stuff.

License

The MIT License (MIT). Please see License File for more information.