diff --git a/lib/Service/ContactsService.php b/lib/Service/ContactsService.php
index 75c2e2552..825092673 100644
--- a/lib/Service/ContactsService.php
+++ b/lib/Service/ContactsService.php
@@ -10,83 +10,108 @@
 class ContactsService {
 
 
-	public function isSystemBook(array $r): bool {
+	/**
+	 * @param array $contact
+	 * @return bool
+	 */
+	public function isSystemBook(array $contact): bool {
 		// Information about system users is fetched via DAV nowadays
 		return (isset($contact['isLocalSystemBook']) && $contact['isLocalSystemBook'] === true);
 	}
 
-	public function hasEmail(array $r): bool {
-		return !isset($r['EMAIL']);
+	/**
+	 * @param array $contact
+	 * @return bool
+	 */
+	public function hasEmail(array $contact): bool {
+		return isset($contact['EMAIL']);
 	}
 
 	/**
 	 * Extract name from an array containing a contact's information
 	 *
-	 * @param array $r
+	 * @param array $contact
 	 * @return string
 	 */
-	public function getNameFromContact(array $r): string {
-		return $r['FN'] ?? '';
+	public function getNameFromContact(array $contact): string {
+		return $contact['FN'] ?? '';
 	}
 
 	/**
 	 * Get photo uri from contact
 	 *
-	 * @param string $raw
+	 * @param array $contact
 	 * @return string|null
 	 */
-	public function getPhotoUri(array $r): ?string {
-		if (!isset($r['PHOTO'])) {
+	public function getPhotoUri(array $contact): ?string {
+		if (!isset($contact['PHOTO'])) {
 			return null;
 		}
 
-		$raw = $r['PHOTO'];
+		$raw = $contact['PHOTO'];
 		$uriPrefix = 'VALUE=uri:';
 		if (str_starts_with($raw, $uriPrefix)) {
-			return substr($raw, strpos($raw, 'http'));
+			$strpos = strpos($raw, 'http');
+			return $strpos !== false ? substr($raw, $strpos) : null;
 		}
 
 		return null;
 	}
 
-	public function getEmail(array $r): array {
-		if (\is_string($r['EMAIL'])) {
-			return [$r['EMAIL']];
+	/**
+	 * @param array $contact
+	 * @return string[]
+	 */
+	public function getEmail(array $contact): array {
+		if (\is_string($contact['EMAIL'])) {
+			return [$contact['EMAIL']];
 		}
-		return $r['EMAIL'];
+		return $contact['EMAIL'];
 	}
 
-	public function getTimezoneId(array $r): ?string {
-		if (!isset($r['TZ'])) {
+	/**
+	 * @param array $contact
+	 * @return string|null
+	 */
+	public function getTimezoneId(array $contact): ?string {
+		if (!isset($contact['TZ'])) {
 			return null;
 		}
 
-		if (\is_array($r['TZ'])) {
-			return $r['TZ'][0];
+		if (\is_array($contact['TZ'])) {
+			return $contact['TZ'][0];
 		}
-		return $r['TZ'];
+		return $contact['TZ'];
 	}
 
-	public function getLanguageId(array $r): ?string {
-		if (!isset($r['LANG'])) {
+	/**
+	 * @param array $contact
+	 * @return string|null
+	 */
+	public function getLanguageId(array $contact): ?string {
+		if (!isset($contact['LANG'])) {
 			return null;
 		}
 
-		if (\is_array($r['LANG'])) {
-			return $r['LANG'][0];
+		if (\is_array($contact['LANG'])) {
+			return $contact['LANG'][0];
 		}
-		return $r['LANG'];
+		return $contact['LANG'];
 	}
 
+	/**
+	 * @param array $groups
+	 * @param string $search
+	 * @return array
+	 */
 	public function filterGroupsWithCount(array $groups, string $search): array {
 		//filter to be unique
-		$categoryMem = [];
+		$categories = [];
 		foreach ($groups as $group) {
-			$categoryNames = explode(',', $group['CATEGORIES']);
-			$categoryMem[] = array_filter($categoryNames, static function ($cat) use ($search) {
+			$categories[] = array_filter(explode(',', $group['CATEGORIES']), static function ($cat) use ($search) {
 				return str_contains(strtolower($cat), $search);
 			});
 		}
-		return array_count_values(array_merge(...$categoryMem));
+		return array_count_values(array_merge(...$categories));
 	}
 }
diff --git a/tests/php/unit/Service/ContactsServiceTest.php b/tests/php/unit/Service/ContactsServiceTest.php
new file mode 100644
index 000000000..986573f92
--- /dev/null
+++ b/tests/php/unit/Service/ContactsServiceTest.php
@@ -0,0 +1,96 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: 2014 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+namespace OCA\Calendar\Service;
+
+use ChristophWurst\Nextcloud\Testing\TestCase;
+
+class ContactsServiceTest extends TestCase {
+	private ContactsService $service;
+
+	public function setUp(): void {
+		$this->service = new ContactsService();
+	}
+
+	public function testGetEmail(): void {
+		$contact = ['EMAIL' => 'test@test.com'];
+		$this->assertEquals(['test@test.com'], $this->service->getEmail($contact));
+	}
+
+	public function testIsSystemBook(): void {
+		$contact = ['isLocalSystemBook' => true];
+		$this->assertTrue($this->service->isSystemBook($contact));
+	}
+
+	public function testIsNotSystemBook(): void {
+		$contact = ['isLocalSystemBook' => false];
+		$this->assertFalse($this->service->isSystemBook($contact));
+	}
+
+	public function testNotSetSystemBook(): void {
+		$this->assertFalse($this->service->isSystemBook([]));
+	}
+
+	public function testHasEmail(): void {
+		$contact = ['EMAIL' => 'test@test.com'];
+		$this->assertTrue($this->service->hasEmail($contact));
+	}
+
+	public function testHasNoEmail(): void {
+		$this->assertFalse($this->service->hasEmail([]));
+	}
+
+	public function testGetPhotoUri(): void {
+		$contact = ['PHOTO' => 'VALUE=uri:http://test'];
+		$this->assertEquals('http://test', $this->service->getPhotoUri($contact));
+	}
+
+	public function testGetPhotoInvalidUri(): void {
+		$contact = ['PHOTO' => 'VALUE=uri:thisisnotit'];
+		$this->assertNull($this->service->getPhotoUri($contact));
+	}
+
+	public function testGetPhotoUriNoPhoto(): void {
+		$this->assertNull($this->service->getPhotoUri([]));
+	}
+
+	public function testFilterGroupsWithCount(): void {
+		$contact = [
+			['CATEGORIES' => 'The Proclaimers,I\'m gonna be,When I go out,I would walk 500 Miles,I would walk 500 more'],
+			['CATEGORIES' => 'The Proclaimers,When I\'m lonely,I would walk 500 Miles,I would walk 500 more'],
+		];
+
+		$searchterm = 'walk';
+
+		$expected = [
+			'I would walk 500 Miles' => 2,
+			'I would walk 500 more' => 2,
+		];
+
+		$this->assertEqualsCanonicalizing($expected, $this->service->filterGroupsWithCount($contact, $searchterm));
+	}
+
+	public function testGetTimezoneId(): void {
+		$contact = ['TZ' => ['UTC']];
+		$this->assertEquals('UTC', $this->service->getTimezoneId($contact));
+	}
+
+	public function testGetLanguageId(): void {
+		$contact = ['LANG' => ['de_de']];
+		$this->assertEquals('de_de', $this->service->getLanguageId($contact));
+	}
+
+	public function testGetNameFromContact(): void {
+		$contact = ['FN' => 'test'];
+		$this->assertEquals('test', $this->service->getNameFromContact($contact));
+	}
+	
+	public function testGetNameFromContactNoName(): void {
+		$this->assertEquals('', $this->service->getNameFromContact([]));
+	}
+}