Interactive installer tests are starting off a clean slate; there is no settings.php that would replace the mail handler with a mail collector.
Every interactive installer test (InstallerTestBase) actually sends out an email to admin@example.com.
We do not want to add a settings.php, because that would tamper the #1 test case of installer tests in which no settings.php exists yet.
Instead, work around the problem in the installer itself to not send out an email when operating in a test site environment:
if (!DRUPAL_TEST_IN_CHILD_SITE) {
send_mail();
}
That way, we can still test an empty installer environment — we only cannot test that the installer sends out an e-mail, but that's an acceptable trade-off.
Closed: outdated
9.5
The change is currently missing an automated test that fails when run with the original code, and succeeds when the bug has been fixed.
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
This was fixed in #2907728: Installer: Convert system functional tests to phpunit → .
That added this block of code.
// Manually configure the test mail collector implementation to prevent
// tests from sending out emails and collect them in state instead.
$this->container->get('config.factory')
->getEditable('system.mail')
->set('interface.default', 'test_mail_collector')
->save();