Testing redirects in Drupal 8

I'm setting up a controller on Drupal 8 which should redirect to the home page if certain query parameters aren't set. Writing a test to make sure that the redirect happens correctly took longer than expected. After trying a number of different approaches, I finally figured it out.

Normally you would check if a page is the front page using the path matcher service:

$path_matcher = \Drupal::service('path.matcher');
$is_front = $path_matcher->isFrontPage();

This didn't seem to work when running PHPUnit tests though. For some reason, the site was redirecting to /user (despite my controller returning a redirect response to /).

That meant my tests were all failing. I spent most of today trying to track down a solution until I finally came across an issue on Drupal.org: "User cancel link doesn't redirect to the homepage" - not quite what I was looking for, but it was fixed in 8.6-dev, which suggested there might be tests to check the redirect.

There in the patch was a useful assertion to check the current address:

+    // Confirm that the user was redirected to the front page.
+    $this->assertSession()->addressEquals('');

Pop that into my test and it works like a charm:

public function testDirectAccessNoParameters() {
 // If no parameters are provided, expect a redirect.

And the output of my test:

sophie@Belgaer:$ fin phpunit --group=current_tests
WARNING: No swap limit support
PHPUnit 6.5.10 by Sebastian Bergmann and contributors.

. 1 / 1 (100%)

Time: 36.78 seconds, Memory: 914.50MB

OK (1 test, 3 assertions)