diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8357a6c7c..ec82b3eaa 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,9 @@ All notable changes to this project will be documented in this file.
 
 ## [Unreleased]
 
+- [#233](https://github.com/os2display/display-api-service/pull/233)
+  - Added calendar api feed source tests for modifiers.
+  - Changed to use PCRE pattern instead of custom pattern building and fixed modifier bugs for calendar api feed source.
 - [#229](https://github.com/os2display/display-api-service/pull/229)
   - Adds options to set paths to component and admin files from path to the json config file.
 - [#225](https://github.com/os2display/display-api-service/pull/225)
diff --git a/docs/calender-api-feed.md b/docs/calender-api-feed.md
index e6a1ca010..eeab566f5 100644
--- a/docs/calender-api-feed.md
+++ b/docs/calender-api-feed.md
@@ -136,20 +136,19 @@ Modifiers can be set up to modify the output of the feed.
 
 Two types of modifiers are available:
 
-* EXCLUDE_IF_TITLE_NOT_CONTAINS: Removes entries from the feed if the title not contain the trigger word.
-* REPLACE_TITLE_IF_CONTAINS: Changes the title if it contains the trigger word.
+* EXCLUDE_IF_TITLE_NOT_CONTAINS: Removes entries from the feed if the title does not contain the pattern.
+* REPLACE_TITLE_IF_CONTAINS: Changes the title if it contains the pattern.
 
 Parameters:
 
 * type: EXCLUDE_IF_TITLE_NOT_CONTAINS or REPLACE_TITLE_IF_CONTAINS
 * id: Unique identifier for the modifier.
 * title: Display name when showing the modifier in the admin.
-* description: Help text for the modifier.
+* description: Description of the modifier.
 * activateInFeed: Should this filter be optional? If false the rule will always apply.
-* trigger: The string that should trigger the modifier.
-* replacement: The string to replace the title with.
 * removeTrigger: Should the trigger word be filtered from the title?
-* caseSensitive: Should the trigger word be case-sensitive?
+* pattern: The PCRE regular expression. See <https://www.php.net/manual/en/reference.pcre.pattern.syntax.php>.
+* replacement: The string to replace the title with. See <https://www.php.net/manual/en/function.preg-replace.php>.
 
 Examples of modifiers:
 
@@ -161,29 +160,26 @@ Examples of modifiers:
         "title": "Vis kun begivenheder med (liste) i titlen.",
         "description": "Denne mulighed fjerner begivenheder, der IKKE har (liste) i titlen. Den fjerner også (liste) fra titlen.",
         "activateInFeed": true,
-        "trigger": "(liste)",
-        "removeTrigger": true,
-        "caseSensitive": false
+        "pattern": "\/\\(liste\\)\/i",
+        "removeTrigger": true
     },
     {
         "type": "REPLACE_TITLE_IF_CONTAINS",
-        "id": "replaceIfContainsOptaget",
         "activateInFeed": false,
-        "trigger": "(optaget)",
+        "id": "replaceIfContainsOptaget",
+        "pattern": "\/\\(optaget\\)\/i",
         "replacement": "Optaget",
-        "removeTrigger": true,
-        "caseSensitive": false
+        "removeTrigger": true
     },
     {
         "type": "REPLACE_TITLE_IF_CONTAINS",
-        "id": "onlyShowAsOptaget",
         "activateInFeed": true,
+        "id": "onlyShowAsOptaget",
         "title": "Overskriv alle titler med Optaget",
         "description": "Denne mulighed viser alle titler som Optaget.",
-        "trigger": "",
+        "pattern": "\/\/",
         "replacement": "Optaget",
-        "removeTrigger": false,
-        "caseSensitive": false
+        "removeTrigger": false
     }
 ]
 ```
diff --git a/src/Feed/CalendarApiFeedType.php b/src/Feed/CalendarApiFeedType.php
index 37210cf59..471416d65 100644
--- a/src/Feed/CalendarApiFeedType.php
+++ b/src/Feed/CalendarApiFeedType.php
@@ -63,8 +63,6 @@ public function __construct(
     public function getData(Feed $feed): array
     {
         try {
-            $results = [];
-
             $configuration = $feed->getConfiguration();
 
             $enabledModifiers = $configuration['enabledModifiers'] ?? [];
@@ -76,62 +74,28 @@ public function getData(Feed $feed): array
             }
 
             $resources = $configuration['resources'];
-            foreach ($resources as $resource) {
-                $events = $this->getResourceEvents($resource);
-
-                /** @var CalendarEvent $event */
-                foreach ($events as $event) {
-                    $title = $event->title;
-
-                    // Modify title according to event modifiers.
-                    foreach ($this->eventModifiers as $modifier) {
-                        // Make it configurable in the Feed if the modifiers should be enabled.
-                        if ($modifier['activateInFeed'] && !in_array($modifier['id'], $enabledModifiers)) {
-                            continue;
-                        }
-
-                        if (self::EXCLUDE_IF_TITLE_NOT_CONTAINS == $modifier['type']) {
-                            $match = preg_match('/'.$modifier['trigger'].'/'.(!$modifier['caseSensitive'] ? 'i' : ''), $title);
-
-                            if ($modifier['removeTrigger']) {
-                                $title = str_replace($modifier['trigger'], '', $title);
-                            }
-
-                            if (!$match) {
-                                continue;
-                            }
-                        }
-
-                        if (self::REPLACE_TITLE_IF_CONTAINS == $modifier['type']) {
-                            $match = preg_match('/'.$modifier['trigger'].'/'.(!$modifier['caseSensitive'] ? 'i' : ''), $title);
-
-                            if ($modifier['removeTrigger']) {
-                                $title = str_replace($modifier['trigger'], '', $title);
-                            }
-
-                            if ($match) {
-                                $title = $modifier['replacement'];
-                            }
-                        }
-                    }
 
-                    $title = trim($title);
+            $events = [];
 
-                    $results[] = [
-                        'id' => Ulid::generate(),
-                        'title' => $title,
-                        'startTime' => $event->startTimeTimestamp,
-                        'endTime' => $event->endTimeTimestamp,
-                        'resourceTitle' => $event->resourceDisplayName,
-                        'resourceId' => $event->resourceId,
-                    ];
-                }
+            foreach ($resources as $resource) {
+                $events += $this->getResourceEvents($resource);
             }
 
+            $modifiedResults = static::applyModifiersToEvents($events, $this->eventModifiers, $enabledModifiers);
+
+            $resultsAsArray = array_map(fn (CalendarEvent $event) => [
+                'id' => Ulid::generate(),
+                'title' => $event->title,
+                'startTime' => $event->startTimeTimestamp,
+                'endTime' => $event->endTimeTimestamp,
+                'resourceTitle' => $event->resourceDisplayName,
+                'resourceId' => $event->resourceId,
+            ], $modifiedResults);
+
             // Sort bookings by start time.
-            usort($results, fn (array $a, array $b) => $a['startTime'] > $b['startTime'] ? 1 : -1);
+            usort($resultsAsArray, fn (array $a, array $b) => $a['startTime'] > $b['startTime'] ? 1 : -1);
 
-            return $results;
+            return $resultsAsArray;
         } catch (\Throwable $throwable) {
             $this->logger->error('{code}: {message}', [
                 'code' => $throwable->getCode(),
@@ -142,6 +106,54 @@ public function getData(Feed $feed): array
         return [];
     }
 
+    public static function applyModifiersToEvents(array $events, array $eventModifiers, array $enabledModifiers): array
+    {
+        $results = [];
+
+        /** @var CalendarEvent $event */
+        foreach ($events as $event) {
+            $title = $event->title;
+
+            // Modify title according to event modifiers.
+            foreach ($eventModifiers as $modifier) {
+                // Make it configurable in the Feed if the modifiers should be enabled.
+                if ($modifier['activateInFeed'] && !in_array($modifier['id'], $enabledModifiers)) {
+                    continue;
+                }
+
+                $pattern = $modifier['pattern'];
+
+                if (self::EXCLUDE_IF_TITLE_NOT_CONTAINS == $modifier['type']) {
+                    $match = preg_match($pattern, $title);
+
+                    if (!$match) {
+                        continue 2;
+                    }
+
+                    if ($modifier['removeTrigger']) {
+                        $title = preg_replace($pattern, '', $title);
+                    }
+                }
+
+                if (self::REPLACE_TITLE_IF_CONTAINS == $modifier['type']) {
+                    $match = preg_match($pattern, $title);
+
+                    if ($match) {
+                        $title = $modifier['replacement'];
+                    }
+                }
+            }
+
+            $title = trim($title);
+
+            $event->title = $title;
+
+            $results[] = $event;
+        }
+
+        return $results;
+    }
+
     /**
      * {@inheritDoc}
      */
diff --git a/tests/Feed/CalendarApiFeedTypeData.php b/tests/Feed/CalendarApiFeedTypeData.php
new file mode 100644
index 000000000..6b997f50f
--- /dev/null
+++ b/tests/Feed/CalendarApiFeedTypeData.php
@@ -0,0 +1,79 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Feed;
+
+use App\Model\CalendarEvent;
+
+class CalendarApiFeedTypeData
+{
+    public array $events = [];
+    public array $modifiers = [];
+
+    public function __construct()
+    {
+        $this->events[] = new CalendarEvent(
+            'id1',
+            'title1',
+            1,
+            2,
+            'resourse1',
+            'Resource 1'
+        );
+        $this->events[] = new CalendarEvent(
+            'id2',
+            'title2 (optaget)',
+            3,
+            4,
+            'resourse1',
+            'Resource 1'
+        );
+        $this->events[] = new CalendarEvent(
+            'id3',
+            'title3 (lISTe)',
+            5,
+            6,
+            'resourse1',
+            'Resource 1'
+        );
+        $this->events[] = new CalendarEvent(
+            'id4',
+            'title4 (lISTe) (optaGET)',
+            7,
+            8,
+            'resourse1',
+            'Resource 1'
+        );
+
+        $this->modifiers[] = [
+            'type' => 'EXCLUDE_IF_TITLE_NOT_CONTAINS',
+            'id' => 'excludeIfNotContainsListe',
+            'title' => 'Vis kun begivenheder med (liste) i titlen.',
+            'description' => 'Denne mulighed fjerner begivenheder, der IKKE har (liste) i titlen. Den fjerner også (liste) fra titlen.',
+            'activateInFeed' => true,
+            'pattern' => '/\(liste\)/i',
+            'removeTrigger' => true,
+        ];
+
+        $this->modifiers[] = [
+            'type' => 'REPLACE_TITLE_IF_CONTAINS',
+            'activateInFeed' => false,
+            'id' => 'replaceIfContainsOptaget',
+            'pattern' => '/\(optaget\)/i',
+            'replacement' => 'Optaget',
+            'removeTrigger' => true,
+        ];
+
+        $this->modifiers[] = [
+            'type' => 'REPLACE_TITLE_IF_CONTAINS',
+            'activateInFeed' => true,
+            'id' => 'onlyShowAsOptaget',
+            'title' => 'Overskriv alle titler med Optaget',
+            'description' => 'Denne mulighed viser alle titler som Optaget.',
+            'pattern' => '//',
+            'replacement' => 'Optaget',
+            'removeTrigger' => false,
+        ];
+    }
+}
diff --git a/tests/Feed/CalendarApiFeedTypeTest.php b/tests/Feed/CalendarApiFeedTypeTest.php
new file mode 100644
index 000000000..ba4a9c525
--- /dev/null
+++ b/tests/Feed/CalendarApiFeedTypeTest.php
@@ -0,0 +1,40 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Feed;
+
+use App\Feed\CalendarApiFeedType;
+use App\Tests\AbstractBaseApiTestCase;
+
+class CalendarApiFeedTypeTest extends AbstractBaseApiTestCase
+{
+    public function testApplyModifiersToEvents(): void
+    {
+        $data = new CalendarApiFeedTypeData();
+
+        $result = CalendarApiFeedType::applyModifiersToEvents($data->events, $data->modifiers, ['excludeIfNotContainsListe']);
+
+        $this->assertEquals(2, count($result));
+        $this->assertEquals('title3', $result[0]->title);
+        $this->assertEquals('Optaget', $result[1]->title);
+
+        $data = new CalendarApiFeedTypeData();
+
+        $result = CalendarApiFeedType::applyModifiersToEvents($data->events, $data->modifiers, ['onlyShowAsOptaget']);
+
+        $this->assertEquals(4, count($result));
+        $this->assertEquals('Optaget', $result[0]->title);
+        $this->assertEquals('Optaget', $result[1]->title);
+        $this->assertEquals('Optaget', $result[2]->title);
+        $this->assertEquals('Optaget', $result[3]->title);
+
+        $data = new CalendarApiFeedTypeData();
+
+        $result = CalendarApiFeedType::applyModifiersToEvents($data->events, $data->modifiers, ['excludeIfNotContainsListe', 'onlyShowAsOptaget']);
+
+        $this->assertEquals(2, count($result));
+        $this->assertEquals('Optaget', $result[0]->title);
+        $this->assertEquals('Optaget', $result[1]->title);
+    }
+}