Add first unit test.

.gitignore

@@ -1,10 +1,15 @@
 .vscode
 .DS_Store
 
+# PHP Unit tests
+phpunit
+.phpunit.result.cache
+
+# Filesystem storage items
 *.sqlite
 *.txt
-
-/docker-compose.yml
-init_complete
 storage/upload/css
+
+# Testing stuff
+/docker-compose.yml
 scratch

tests/Framework/Util/UtilTest.php

@@ -0,0 +1,31 @@
+<?php
+use PHPUnit\Framework\TestCase;
+
+final class UtilTest extends TestCase
+{
+    public function testRelativeTime(): void
+    {
+        $datetime = new DateTimeImmutable();
+
+        $oneMinuteAgo = $datetime->modify('-1 minute')->format('c');
+        $relativeTime = Util::relative_time($oneMinuteAgo);
+        $this->assertSame($relativeTime, "1 minute ago");
+
+        $twoHoursAgo = $datetime->modify('-2 hours')->format('c');
+        $relativeTime = Util::relative_time($twoHoursAgo);
+        $this->assertSame($relativeTime, "2 hours ago");
+
+        $threeDaysAgo = $datetime->modify('-3 days')->format('c');
+        $relativeTime = Util::relative_time($threeDaysAgo);
+        $this->assertSame($relativeTime, "3 days ago");
+
+        $fourMonthsAgo = $datetime->modify('-4 months')->format('c');
+        $relativeTime = Util::relative_time($fourMonthsAgo);
+        $this->assertSame($relativeTime, "4 months ago");
+
+        $fiveYearsAgo = $datetime->modify('-5 years')->format('c');
+        $relativeTime = Util::relative_time($fiveYearsAgo);
+        $this->assertSame($relativeTime, "5 years ago");
+
+    }
+}