How to Update Hundreds of Test Fixtures with Single PHPUnit run

In previous post, we look at the benefits of visual snapshot testing for lazy people. How bare input/output code in a single file makes tests easy to read for new contributors.

Today, we look at how to maintain visual snapshot tests.

Let's say we need to add declare(strict_types=1); to output part of 100 test fixtures? Would you add it manually in every single file?

Short quiz from last week: what is the visual snapshot test?

A test where the new test case is a single fixture file:


Let's say we test a service that multiplies the input number by 5.

How would the fixture look like?


Correct! Now let's learn something new.

"It's easy to write tests that are hard to maintain."

Use Case: Add 1 Line to 100 Files

I'm currently working on a tool that migrates YAML configs to PHP. It's almost finished... but there is one thing missing in all those configs. PHP configs.

I forgot to add the declare(strict_types=1); line. So now, every time you generate a PHP config, you have to run coding standards too on these files. So much extra work you, end-developers.

When was my mission changed to adding developers extra tedious work? We need to handle it.

What Can We Do Now?

  • add it to the PHP script, that converts the file to PHP, so the line is there
  • now tests start failing because the line is missing in the expected output
    key: 'value'

use Symfony\Component\DependencyInjection\Loader\Configurator\ContainerConfigurator;

return function (ContainerConfigurator $containerConfigurator): void {
    $parameters = $containerConfigurator->parameters();

    $parameters->set('key', 'value');
  • go through test fixtures and manually add the line

If we are lucky and the pattern is unique, we can use PHPStorm find/replace or even regular expressions. This might work for this simple case, but soon fails for real-life cases like "add extra method call under each $service->set()".

We can do better.

Automated Test Fixture Updates

  • How can we automate the update under few seconds?
  • How can we do it without thinking about what needs to be changed and how?

With visual snapshot tests this is piece of cake. All we need is UPDATE_TESTS=1 env and normal PHPUnit run:

Now, all the 100 files have completed declare(strict_types=1);:

    key: 'value'


use Symfony\Component\DependencyInjection\Loader\Configurator\ContainerConfigurator;

return function (ContainerConfigurator $containerConfigurator): void {
    $parameters = $containerConfigurator->parameters();

    $parameters->set('key', 'value');

How did that Happened?

In the previous post, we looked on how to split and test fixture files.

We only update this code with a single method, that will handle the fixture updates:


 use PHPUnit\Framework\TestCase;

 final class FirstTryTest extends TestCase
     public function test(): void
         $filePath = __DIR__ . '/fixture/first_try.php';

         $fixtureContent = file_get_contents($filePath);
         [$input, $expectedOutput] = explode("\n-----\n", $fixtureContent);

         // test your main domain service
         $output = $this->processInputInYourDomain($input);

+        $this->updateFixture($input, $output, $filePath);

         $this->assertSame($expectedOutput, $output);

And add the updateFixture() method:

private function updateFixture(
    string $input,
    string $currentOutput,
    string $fixtureFilePath
): void {
    // only runs when UPDATE_TESTS=1 is put before PHPUnit run
    if (! getenv('UPDATE_TESTS')) {

    // update changed output content part
    $newOriginalContent = $input . PHP_EOL .
        '-----' . PHP_EOL .
        $currentOutput . PHP_EOL;

    // update the fixture file
    file_put_contents($fixtureFilePath, $newOriginalContent);

And that's it!

The best place to add updateFixture() is an abstract test case, e.g., AbstractVisualSnapshotTestCase. So we have one place to change.

Now you can do massive changes in your business logic, and even you rewrite the output completely, all you need to run is:

UPDATE_TESTS=1 vendor/bin/phpunit

Now we know the simplest way to maintain tests that are easy to read there is... or is it?

Happy coding!

Do you learn from my contents or use open-souce packages like Rector every day?
Consider supporting it on GitHub Sponsors. I'd really appreciate it!