Snapshot testing is a way to test without writing actual test cases.
You can learn more in this free video from our Testing Laravel course. Don't worry you can use this package in non-Laravel projects too.
use Spatie\Snapshots\MatchesSnapshots;
class OrderTest
{
use MatchesSnapshots;
public function 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!
$orderId = new Order(2); // Regression! Was `1`> ./vendor/bin/phpunit
1) OrderTest::test_it_casts_to_json
Failed asserting that two strings are equal.
--- Expected
+++ Actual
@@ @@
Failed asserting that '{"id":2}' matches JSON string "{
"id": 1
}
FAILURES!
Tests: 1, Assertions: 1, Failures: 1.
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You can install the package via composer:
composer require --dev spatie/phpunit-snapshot-assertionsTo make snapshot assertions, use the Spatie\Snapshots\MatchesSnapshots trait in your test case class. This adds a set of assertion methods to the class:
assertMatchesSnapshot($actual)assertMatchesFileHashSnapshot($actual)assertMatchesFileSnapshot($actual)assertMatchesHtmlSnapshot($actual)assertMatchesJsonSnapshot($actual)assertMatchesObjectSnapshot($actual)assertMatchesTextSnapshot($actual)assertMatchesXmlSnapshot($actual)assertMatchesYamlSnapshot($actual)assertMatchesImageSnapshot($actual)
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 plain text or YAML representation of the actual value.
fooLet'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() {
$this->assertMatchesSnapshot('bar');
}> ./vendor/bin/phpunit
1) ExampleTest::test_it_matches_a_string
Failed asserting that two strings are equal.
--- Expected
+++ Actual
@@ @@
-'foo'
+'bar'
FAILURES!
Tests: 1, Assertions: 1, Failures: 1.
When we expect a changed value, we need to tell the test runner to update the existing snapshots instead of failing the test. This is possible by adding a-d --update-snapshots flag to the phpunit command, or setting the UPDATE_SNAPSHOTS env var to true.
> ./vendor/bin/phpunit -d --update-snapshots
OK (1 test, 1 assertion)
As a result, our snapshot file returns "bar" instead of "foo".
barThe MatchesSnapshots trait offers two ways to assert that a file is identical to the snapshot that was made the first time the test was run:
The assertMatchesFileHashSnapshot($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.
The assertImageSnapshot requires the spatie/pixelmatch-php package to be installed.
This assertion will pass if the given image is nearly identical to the snapshot that was made the first time the test was run. You can customize the threshold by passing a second argument to the assertion. Higher values will make the comparison more sensitive. The threshold should be between 0 and 1.
$this->assertMatchesImageSnapshot($imagePath, 0.1);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.
protected function getSnapshotId(): string
{
return (new ReflectionClass($this))->getShortName().'--'.
$this->name().'--'.
$this->snapshotIncrementor;
}By default, snapshots are stored in a __snapshots__ directory relative to the test class. This can be changed by overriding the getSnapshotDirectory method.
protected function getSnapshotDirectory(): string
{
return dirname((new ReflectionClass($this))->getFileName()).
DIRECTORY_SEPARATOR.
'snapshots';
}The driver used to serialize the data can be specificied as second argument of the
assertMatchesSnapshot method, so you can pick one that better suits your needs:
use Spatie\Snapshots\Drivers\JsonDriver;
use Spatie\Snapshots\MatchesSnapshots;
class OrderTest
{
use MatchesSnapshots;
public function test_snapshot_with_json_driver()
{
$order = new Order(1);
$this->assertMatchesSnapshot($order->toJson(), new JsonDriver());
}
}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
serializemethod returns a string which will be written to the snapshot file. In theJsonDriver, 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
jsonas 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
assertJsonStringEqualsJsonStringmethod.
Drivers can be used by passing them as assertMatchesSnapshot's second argument.
$this->assertMatchesSnapshot($something->toYaml(), new MyYamlDriver());When running your tests in Continuous Integration you would possibly want to disable the creation of snapshots.
By using the --without-creating-snapshots parameter or by setting the CREATE_SNAPSHOTS env var to false, PHPUnit will fail if the snapshots don't exist.
> ./vendor/bin/phpunit -d --without-creating-snapshots
1) ExampleTest::test_it_matches_a_string
Snapshot "ExampleTest__test_it_matches_a_string__1.txt" does not exist.
You can automatically create it by removing the `CREATE_SNAPSHOTS=false` env var, or `-d --no-create-snapshots` of PHPUnit's CLI arguments.If you want to run your test in parallel with a tool like Paratest, ou with the php artisan test --parallel command of Laravel, you will have to use the environment variables.
> CREATE_SNAPSHOTS=false php artisan test --parallel
1) ExampleTest::test_it_matches_a_string
Snapshot "ExampleTest__test_it_matches_a_string__1.txt" does not exist.
You can automatically create it by removing the `CREATE_SNAPSHOTS=false` env var, or `-d --no-create-snapshots` of PHPUnit's CLI arguments.Windows users should configure their line endings in .gitattributes.
# Snapshots used in tests hold serialized data and their line ending should be left unchanged
tests/**/__snapshots__/** binaryPlease see CHANGELOG for more information what has changed recently.
composer testPlease see CONTRIBUTING for details.
If you've found a bug regarding security please mail security@spatie.be instead of using the issue tracker.
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The MIT License (MIT). Please see License File for more information.