test assignment completion

backend/tests/Unit/Schedule/ScheduleAssignmentTest.php

@@ -0,0 +1,49 @@
+<?php
+
+namespace Tests\Unit\Schedule;
+
+use App\Schedule\ScheduleAssignment;
+use DateTimeImmutable;
+use DateTimeZone;
+use PHPUnit\Framework\TestCase;
+
+class ScheduleAssignmentTest extends TestCase
+{
+    public function test_it_completes_only_once_until_reopened(): void
+    {
+        $assignment = $this->assignment();
+        $firstCompletion = $this->utc('2026-08-15T12:00:00');
+        $laterCompletion = $this->utc('2026-08-15T13:00:00');
+
+        $assignment->complete($firstCompletion);
+        $assignment->complete($laterCompletion);
+
+        $this->assertSame($firstCompletion, $assignment->getCompletedAt());
+
+        $assignment->reopen();
+
+        $this->assertNull($assignment->getCompletedAt());
+
+        $assignment->complete($laterCompletion);
+
+        $this->assertSame($laterCompletion, $assignment->getCompletedAt());
+    }
+
+    private function assignment(): ScheduleAssignment
+    {
+        return new ScheduleAssignment(
+            id: 1,
+            name: 'Lesson',
+            kind: 'lesson',
+            path: ['Course', 'Lesson'],
+            scheduledDate: $this->utc('2026-08-15'),
+            position: 1,
+            completedAt: null,
+        );
+    }
+
+    private function utc(string $value): DateTimeImmutable
+    {
+        return new DateTimeImmutable($value, new DateTimeZone('UTC'));
+    }
+}