How to test asynchronous code in PHPUnit?

@arnoldo.moen 

To test asynchronous code in PHPUnit, you can use the Generator feature. Here's a step-by-step guide on how to do it:

1. Update PHPUnit to version 9.4 or above, as earlier versions do not support asynchronous testing.
2. Define a test case class that extends PHPUnitFrameworkTestCase (if you don't have one already).
3. Define an asynchronous test method with the prefix test and suffix Async. For example, testAsyncExample().
4. Convert the test method into a generator function by adding a yield statement before each asynchronous call. This will pause the execution until the asynchronous call is complete. You can use the yield statement as many times as necessary.

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public function testAsyncExample(): Generator
{
    $promisor = new Promisor();
    yield $promisor->doAsyncTask();
    // more async calls using yield
}

1. Use PHPUnit's runTestInSeparateProcess() annotation to ensure that the test method is run in a separate process. This is necessary for handling parallel processing.

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/**
 * @runInSeparateProcess
 */
public function testAsyncExample(): Generator
{
    // test code
}

1. In the test method, use the assertXxx() methods provided by PHPUnit to perform assertions on the asynchronously generated results.

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public function testAsyncExample(): Generator
{
    $promisor = new Promisor();
    $result = yield $promisor->doAsyncTask();
    $this->assertEquals('expected', $result);
}

1. Run the test case with PHPUnit using the following command:

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vendor/bin/phpunit --testsuite suiteName

Make sure to replace suiteName with the appropriate name of your test suite.

By following these steps, PHPUnit will be able to handle asynchronous code testing with ease.