test: add the first assertion

tests/EventRepositoryTest.php

@@ -7,7 +7,13 @@ use Symfony\Bundle\FrameworkBundle\Test\KernelTestCase;
 final class EventRepositoryTest extends KernelTestCase
 {
     /** @test */
-    public function should_only_return_attendees_with_a_yes_rsvp(): array {
-        return [];
+    public function should_only_return_attendees_with_a_yes_rsvp(): void {
+        $attendees = [
+            ['name' => 'Matthew Setter'],
+            ['name' => 'Matthew Setter'],
+            ['name' => 'Matthew Setter'],
+        ];
+
+        $this->assertCount(3, $attendees);
     }
 }