diff --git a/.forgejo/workflows/phpunit.yml b/.forgejo/workflows/phpunit.yml
index 23321d9..a576ee2 100644
--- a/.forgejo/workflows/phpunit.yml
+++ b/.forgejo/workflows/phpunit.yml
@@ -37,7 +37,7 @@ jobs:
           path: |
             ${{ env.WP_CORE_DIR }}
             ${{ env.WP_TESTS_DIR }}
-          key: cache-wordpress-3
+          key: cache-wordpress-4
 
       - name: Cache Composer
         id: cache-composer-phpunit
@@ -74,7 +74,22 @@ jobs:
         if: steps.cache-wordpress.outputs.cache-hit != 'false'
         run: bash bin/install-wp-tests.sh wordpress_test root root 127.0.0.1 6.6 false true true true
 
-      - name: Run PHPUnit
-        run: cd /workspace/Event-Federation/wordpress-activitypub-event-extensions/ && ./vendor/bin/phpunit
+      - name: Run Integration tests for The Events Calendar
+        run: cd /workspace/Event-Federation/wordpress-activitypub-event-extensions/ && ./vendor/bin/phpunit --filter=the_events_calendar
         env:
           PHP_VERSION: ${{ matrix.php-version }}
+
+      - name: Run Integration tests for VS Event List
+        run: cd /workspace/Event-Federation/wordpress-activitypub-event-extensions/ && ./vendor/bin/phpunit --filter=vs_event_list
+        env:
+          PHP_VERSION: ${{ matrix.php-version }}
+
+      - name: Run Integration tests for GatherPress
+        run: cd /workspace/Event-Federation/wordpress-activitypub-event-extensions/ && ./vendor/bin/phpunit --filter=gatherpress
+        env:
+          PHP_VERSION: ${{ matrix.php-version }}
+
+      - name: Run Integration tests for Events Manager
+        run: cd /workspace/Event-Federation/wordpress-activitypub-event-extensions/ && ./vendor/bin/phpunit --filter=events_manager
+        env:
+          PHP_VERSION: ${{ matrix.php-version }}
\ No newline at end of file
diff --git a/bin/install-wp-tests.sh b/bin/install-wp-tests.sh
index ff43d3a..8d495bf 100755
--- a/bin/install-wp-tests.sh
+++ b/bin/install-wp-tests.sh
@@ -209,7 +209,12 @@ install_wp_plugin() {
 
 	# Get the latest tag.
     LATEST_TAG=$(svn log https://plugins.svn.wordpress.org/$PLUGIN_NAME/tags --limit 1 | awk 'NR == 4 { print $4 }')
-	PLUGIN_FILE="$PLUGIN_NAME.$LATEST_TAG.zip"
+	if [ -n "$LATEST_TAG" ]; then
+		PLUGIN_FILE="$PLUGIN_NAME.$LATEST_TAG.zip"
+	else
+		PLUGIN_FILE="$PLUGIN_NAME.zip"
+	fi
+
 	URL="https://downloads.wordpress.org/plugin/$PLUGIN_FILE"
 
     # Check if the plugin file already exists
@@ -226,16 +231,13 @@ install_wp_plugins() {
         echo "Skipping WordPress plugin installation."
         return 0
     fi
-	# Always install the ActivityPub plugin.
+	# Install the one and only ActivityPub plugin (greetings @pfefferle).
 	install_wp_plugin activitypub
+	# Install (not-activate) all supported event plugins.
 	install_wp_plugin the-events-calendar
-	# Install additional plugins.
-	# if [[ -n "$PLUGINS" ]]; then
-	# 	IFS=',' read -ra PLUGIN_ARRAY <<< "$PLUGINS"
-	# 	for plugin in "${PLUGIN_ARRAY[@]}"; do
-	# 		install_wp_plugin "$plugin"
-	# 	done
-	# fi
+	install_wp_plugin very-simple-event-list
+	install_wp_plugin gatherpress
+	install_wp_plugin events-manager
 }
 
 install_wp
diff --git a/composer.json b/composer.json
index ba5b52a..d091876 100644
--- a/composer.json
+++ b/composer.json
@@ -41,10 +41,24 @@
         "lint:fix": [
             "vendor/bin/phpcbf"
         ],
-        "test": [
+        "prepare-test": [
             "composer install",
-            "bin/install-wp-tests.sh wordpress-test root wordpress-test test-db latest true",
-            "phpunit"
-        ]
+            "bin/install-wp-tests.sh wordpress-test root wordpress-test test-db latest true"
+        ],
+        "test": [
+            "@prepare-test",
+            "@test-vs-event-list",
+            "@test-the-events-calendar",
+            "@test-gatherpress",
+            "@test-events-manager"
+        ],
+        "test-debug": [
+            "@prepare-test",
+            "@test-vs-event-list"
+        ],
+        "test-vs-event-list": "phpunit --filter=vs_event_list",
+        "test-the-events-calendar": "phpunit --filter=the_events_calendar",
+        "test-gatherpress": "phpunit --filter=gatherpress",
+        "test-events-manager": "phpunit --filter=events_manager"
     }
 }
diff --git a/docker-compose.yml b/docker-compose.yml
index 47d5117..78aacdd 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -26,10 +26,10 @@ services:
       MARIADB_ROOT_PASSWORD: wordpress-test
     healthcheck:
       test: ["CMD", "healthcheck.sh", "--connect", "--innodb_initialized"]
-      start_period: 5s
-      interval: 4s
+      start_period: 2s
+      interval: 1s
       timeout: 5s
-      retries: 5
+      retries: 10
 
   test-php:
     build:
@@ -42,6 +42,6 @@ services:
       - test-db
     volumes:
       - .:/app
-    command: ["composer", "run-script", "test"]
+    command: ["composer", "run-script", "test-debug"]
     extra_hosts:
       - "host.docker.internal:host-gateway"
diff --git a/includes/activitypub/transformer/class-event.php b/includes/activitypub/transformer/class-event.php
index 67c8cf7..4dc96e1 100644
--- a/includes/activitypub/transformer/class-event.php
+++ b/includes/activitypub/transformer/class-event.php
@@ -35,7 +35,7 @@ class Event extends Post {
 	 *
 	 * @return string The User-URL.
 	 */
-	protected function get_actor() {
+	protected function get_actor(): ?string {
 		return $this->get_attributed_to();
 	}
 
@@ -46,10 +46,17 @@ class Event extends Post {
 	 *
 	 * @return string The Event Object-Type.
 	 */
-	protected function get_type() {
+	protected function get_type(): string {
 		return 'Event';
 	}
 
+	/**
+	 * Get a sane default for whether comments are enabled.
+	 */
+	protected function get_comments_enabled(): ?bool {
+		return comments_open( $this->wp_object );
+	}
+
 	/**
 	 * Returns the title of the event.
 	 *
@@ -57,7 +64,7 @@ class Event extends Post {
 	 *
 	 * @return string The name.
 	 */
-	protected function get_name() {
+	protected function get_name(): string {
 		return $this->wp_object->post_title;
 	}
 
@@ -79,7 +86,7 @@ class Event extends Post {
 	 *
 	 * @return string
 	 */
-	public function get_join_mode() {
+	public function get_join_mode(): ?string {
 		return 'external';
 	}
 
@@ -89,16 +96,16 @@ class Event extends Post {
 	 * Currently we don't handle joins, we always mark events as external.
 	 * We just link back to the events HTML representation on our WordPress site.
 	 *
-	 * @return string|null The external participation URL.
+	 * @return ?string The external participation URL.
 	 */
-	public function get_external_participation_url(): string|null {
+	public function get_external_participation_url(): ?string {
 		return 'external' === $this->get_join_mode() ? $this->get_url() : null;
 	}
 
 	/**
 	 * Set the event category, via the mapping setting.
 	 */
-	public function get_category() {
+	public function get_category(): ?string {
 		$current_category_mapping = \get_option( 'activitypub_event_extensions_event_category_mappings', array() );
 		$terms                    = \get_the_terms( $this->wp_object, $this->wp_taxonomy );
 
@@ -116,7 +123,7 @@ class Event extends Post {
 	 *
 	 * @return Event_Object
 	 */
-	public function to_object() {
+	public function to_object(): Event_Object {
 		$activitypub_object = new Event_Object();
 		$activitypub_object = $this->transform_object_properties( $activitypub_object );
 
diff --git a/includes/activitypub/transformer/class-events-manager.php b/includes/activitypub/transformer/class-events-manager.php
index 487181c..3e95fe0 100644
--- a/includes/activitypub/transformer/class-events-manager.php
+++ b/includes/activitypub/transformer/class-events-manager.php
@@ -94,16 +94,21 @@ final class Events_Manager extends Event_Transformer {
 			return null;
 		}
 
-		$location    = new Place();
 		$em_location = $this->em_event->get_location();
 
+		if ( '' === $em_location->location_id ) {
+			return null;
+		}
+
+		$location = new Place();
 		$location->set_name( $em_location->location_name );
 
 		$address = array(
 			'type'            => 'PostalAddress',
 			'addressCountry'  => $em_location->location_country,
 			'addressLocality' => $em_location->location_town,
-			'streetAddress'   => $em_location->location_address,
+			'postalAddress'   => $em_location->location_address,
+			'postalCode'      => $em_location->location_postcode,
 			'name'            => $em_location->location_name,
 		);
 		if ( $em_location->location_state ) {
@@ -249,8 +254,10 @@ final class Events_Manager extends Event_Transformer {
 
 	/**
 	 * Get the events title/name.
+	 *
+	 * @return string
 	 */
-	protected function get_name() {
+	protected function get_name(): string {
 		return $this->em_event->event_name;
 	}
 
@@ -259,7 +266,7 @@ final class Events_Manager extends Event_Transformer {
 	 *
 	 * @return Activitypub\Activity\Event
 	 */
-	public function to_object() {
+	public function to_object(): Event {
 		$this->em_event     = new EM_Event( $this->wp_object->ID, 'post_id' );
 		$activitypub_object = new Event();
 
diff --git a/includes/activitypub/transformer/class-gatherpress.php b/includes/activitypub/transformer/class-gatherpress.php
index d04e4a6..1bd9081 100644
--- a/includes/activitypub/transformer/class-gatherpress.php
+++ b/includes/activitypub/transformer/class-gatherpress.php
@@ -49,29 +49,18 @@ final class GatherPress extends Event {
 	protected $gp_venue;
 
 	/**
-	 * Get transformer name.
+	 * Extend the constructor, to also set the GatherPress objects.
 	 *
-	 * Retrieve the transformers name.
+	 * This is a special class object form The Events Calendar which
+	 * has a lot of useful functions, we make use of our getter functions.
 	 *
-	 * @since 1.0.0
-	 * @access public
-	 * @return string Widget name.
+	 * @param WP_Post $wp_object The WordPress object.
+	 * @param string  $wp_taxonomy The taxonomy slug of the event post type.
 	 */
-	public function get_transformer_name() {
-		return 'gatherpress/gp-event';
-	}
-
-	/**
-	 * Get transformer title.
-	 *
-	 * Retrieve the transformers label.
-	 *
-	 * @since 1.0.0
-	 * @access public
-	 * @return string Widget title.
-	 */
-	public function get_transformer_label() {
-		return 'GatherPress Event';
+	public function __construct( $wp_object, $wp_taxonomy ) {
+		parent::__construct( $wp_object, $wp_taxonomy );
+		$this->gp_event = new GatherPress_Event( $this->wp_object->ID );
+		$this->gp_venue = $this->gp_event->get_venue_information();
 	}
 
 	/**
@@ -90,15 +79,19 @@ final class GatherPress extends Event {
 	/**
 	 * Get the event location.
 	 *
-	 * @return array The Place.
+	 * @return Place|null The place objector null if not place set.
 	 */
-	public function get_location() {
+	public function get_location(): Place|null {
 		$address = $this->gp_venue['full_address'];
-		$place   = new Place();
-		$place->set_type( 'Place' );
-		$place->set_name( $address );
-		$place->set_address( $address );
-		return $place;
+		if ( $address ) {
+			$place = new Place();
+			$place->set_type( 'Place' );
+			$place->set_name( $address );
+			$place->set_address( $address );
+			return $place;
+		} else {
+			return null;
+		}
 	}
 
 	/**
@@ -134,7 +127,7 @@ final class GatherPress extends Event {
 	/**
 	 * Overrides/extends the get_attachments function to also add the event Link.
 	 */
-	protected function get_attachment() {
+	protected function get_attachment(): array {
 		$attachments = parent::get_attachment();
 		if ( count( $attachments ) ) {
 			$attachments[0]['type'] = 'Document';
@@ -154,7 +147,7 @@ final class GatherPress extends Event {
 	 *
 	 * @return string The User-URL.
 	 */
-	protected function get_attributed_to() {
+	protected function get_attributed_to(): string {
 		$user = new Blog();
 		return $user->get_url();
 	}
@@ -167,7 +160,7 @@ final class GatherPress extends Event {
 	 *
 	 * @return string $summary The custom event summary.
 	 */
-	public function get_summary() {
+	public function get_summary(): string {
 		if ( $this->wp_object->excerpt ) {
 			$excerpt = $this->wp_object->post_excerpt;
 		} elseif ( get_post_meta( $this->wp_object->ID, 'event-summary', true ) ) {
@@ -184,38 +177,31 @@ final class GatherPress extends Event {
 		return $summary;
 	}
 
+	/**
+	 * Get the content.
+	 */
+	public function get_content(): string {
+		return $this->wp_object->post_content;
+	}
+
+	/**
+	 * Determine whether the event is online.
+	 *
+	 * @return bool
+	 */
+	public function get_is_online(): bool {
+		return $this->gp_event->maybe_get_online_event_link() ? true : false;
+	}
+
+
 	/**
 	 * Transform the WordPress Object into an ActivityPub Object.
 	 *
 	 * @return Activitypub\Activity\Event
 	 */
-	public function to_object() {
-		$this->ap_object = new Event_Object();
-		$this->gp_event  = new GatherPress_Event( $this->wp_object->ID );
-		$this->gp_venue  = $this->gp_event->get_venue_information();
+	public function to_object(): Event_Object {
+		$activitypub_object = parent::to_object();
 
-		$this->ap_object = parent::to_object();
-
-		$this->ap_object->set_comments_enabled( 'open' === $this->wp_object->comment_status ? true : false );
-
-		$this->ap_object->set_external_participation_url( $this->get_url() );
-
-		$online_event_link = $this->gp_event->maybe_get_online_event_link();
-
-		if ( $online_event_link ) {
-			$this->ap_object->set_is_online( true );
-		} else {
-			$this->ap_object->set_is_online( false );
-		}
-
-		$this->ap_object->set_status( 'CONFIRMED' );
-
-		$this->ap_object->set_name( get_the_title( $this->wp_object->ID ) );
-
-		$this->ap_object->set_actor( get_rest_url_by_path( 'application' ) );
-		$this->ap_object->set_to( array( 'https://www.w3.org/ns/activitystreams#Public' ) );
-
-		$this->ap_object->set_location();
-		return $this->ap_object;
+		return $activitypub_object;
 	}
 }
diff --git a/includes/activitypub/transformer/class-the-events-calendar.php b/includes/activitypub/transformer/class-the-events-calendar.php
index 6881271..7707ca8 100644
--- a/includes/activitypub/transformer/class-the-events-calendar.php
+++ b/includes/activitypub/transformer/class-the-events-calendar.php
@@ -14,6 +14,7 @@ if ( ! defined( 'ABSPATH' ) ) {
 
 use Activitypub_Event_Extensions\Activitypub\Transformer\Event;
 use Activitypub\Activity\Extended_Object\Place;
+use Activitypub\Activity\Extended_Object\Event as Event_Object;
 use WP_Error;
 use WP_Post;
 
@@ -194,7 +195,7 @@ final class The_Events_Calendar extends Event {
 	 *
 	 * @return Event_Object
 	 */
-	public function to_object() {
+	public function to_object(): Event_Object {
 		$activitypub_object = parent::to_object();
 
 		return $activitypub_object;
diff --git a/includes/activitypub/transformer/class-vs-event-list.php b/includes/activitypub/transformer/class-vs-event-list.php
index 2f0cd56..f6f9b61 100644
--- a/includes/activitypub/transformer/class-vs-event-list.php
+++ b/includes/activitypub/transformer/class-vs-event-list.php
@@ -27,7 +27,6 @@ if ( ! defined( 'ABSPATH' ) ) {
  * @since 1.0.0
  */
 final class VS_Event_List extends Event_Transformer {
-
 	/**
 	 * The target transformer ActivityPub Event object.
 	 *
@@ -35,19 +34,6 @@ final class VS_Event_List extends Event_Transformer {
 	 */
 	protected $ap_object;
 
-	/**
-	 * Get transformer name.
-	 *
-	 * Retrieve the transformers name.
-	 *
-	 * @since 1.0.0
-	 * @access public
-	 * @return string Widget name.
-	 */
-	public function get_transformer_name(): string {
-		return 'activitypub-event-transformers/vs-event';
-	}
-
 	/**
 	 * Returns the ActivityStreams 2.0 Object-Type for an Event.
 	 *
@@ -64,21 +50,28 @@ final class VS_Event_List extends Event_Transformer {
 	 *
 	 * @return Place The Place.
 	 */
-	public function get_location(): Place {
+	public function get_location(): ?Place {
 		$address = get_post_meta( $this->wp_object->ID, 'event-location', true );
-		$place   = new Place();
-		$place->set_type( 'Place' );
-		$place->set_name( $address );
-		$place->set_address( $address );
-		return $place;
+		if ( $address ) {
+			$place = new Place();
+			$place->set_type( 'Place' );
+			$place->set_name( $address );
+			$place->set_address( $address );
+			return $place;
+		} else {
+			return null;
+		}
 	}
 
 	/**
 	 * Get the end time from the events metadata.
 	 */
-	protected function get_end_time(): string {
+	protected function get_end_time(): ?string {
+		if ( 'yes' === get_post_meta( $this->wp_object->ID, 'event-hide-end-time', true ) ) {
+			return null;
+		}
 		$end_time = get_post_meta( $this->wp_object->ID, 'event-date', true );
-		return \gmdate( 'Y-m-d\TH:i:s\Z', $end_time );
+		return $end_time ? \gmdate( 'Y-m-d\TH:i:s\Z', $end_time ) : null;
 	}
 
 	/**
@@ -86,28 +79,32 @@ final class VS_Event_List extends Event_Transformer {
 	 */
 	protected function get_start_time(): string {
 		$start_time = get_post_meta( $this->wp_object->ID, 'event-start-date', true );
-		return \gmdate( 'Y-m-d\TH:i:s\Z', $start_time );
+		return $start_time ? \gmdate( 'Y-m-d\TH:i:s\Z', $start_time ) : null;
 	}
 
 	/**
 	 * Get the event link from the events metadata.
+	 *
+	 * @return ?array Associated array of an ActivityStreams Link object with the events URL.
 	 */
-	private function get_event_link(): array {
-		$event_link = get_post_meta( $this->wp_object->ID, 'event-link', true );
+	private function get_event_link(): ?array {
+		$event_link       = get_post_meta( $this->wp_object->ID, 'event-link', true );
+		$event_link_label = get_post_meta( $this->wp_object->ID, 'event-link-label', true ) ?? 'Event Link';
 		if ( $event_link ) {
 			return array(
 				'type'      => 'Link',
-				'name'      => 'Website',
+				'name'      => $event_link_label,
 				'href'      => \esc_url( $event_link ),
 				'mediaType' => 'text/html',
 			);
 		}
+		return null;
 	}
 
 	/**
 	 * Overrides/extends the get_attachments function to also add the event Link.
 	 */
-	protected function get_attachment() {
+	protected function get_attachment(): ?array {
 		$attachments = parent::get_attachment();
 		if ( count( $attachments ) ) {
 			$attachments[0]['type'] = 'Document';
@@ -128,7 +125,7 @@ final class VS_Event_List extends Event_Transformer {
 	 *
 	 * @return string $summary The custom event summary.
 	 */
-	public function get_summary() {
+	public function get_summary(): ?string {
 		if ( $this->wp_object->excerpt ) {
 			$excerpt = $this->wp_object->post_excerpt;
 		} elseif ( get_post_meta( $this->wp_object->ID, 'event-summary', true ) ) {
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index e32baa7..de49112 100755
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -30,17 +30,54 @@ require_once "{$_tests_dir}/includes/functions.php";
  */
 function _manually_load_plugin() {
 	$plugin_dir = ABSPATH . '/wp-content/plugins/';
+
+	// Always manually load the ActivityPub plugin.
 	require_once $plugin_dir . 'activitypub/activitypub.php';
-	$event_plugin = 'the-events-calendar';
-	switch ( $event_plugin ) {
-		case 'the-events-calendar':
-			$plugin_file = 'the-events-calendar/the-events-calendar.php';
-			require_once $plugin_dir . $plugin_file;
-			$current   = get_option( 'active_plugins', array() );
-			$current[] = $plugin_file;
-			sort( $current );
-			update_option( 'active_plugins', $current );
+
+	// Capture the --filter argument.
+	$activitypub_event_extension_integration_filter = null;
+	foreach ( $_SERVER['argv'] as $arg ) {
+		if ( strpos( $arg, '--filter=' ) === 0 ) {
+			$activitypub_event_extension_integration_filter = substr( $arg, strlen( '--filter=' ) );
+			break;
+		}
 	}
+
+	$plugin_file = null;
+	// See if we want to run integration tests for a specific event-plugin.
+	switch ( $activitypub_event_extension_integration_filter ) {
+		case 'the_events_calendar':
+			$plugin_file = 'the-events-calendar/the-events-calendar.php';
+			break;
+		case 'vs_event_list':
+			$plugin_file = 'very-simple-event-list/vsel.php';
+			break;
+		case 'events_manager':
+			$plugin_file = 'events-manager/events-manager.php';
+			break;
+		case 'gatherpress':
+			$plugin_file = 'gatherpress/gatherpress.php';
+			break;
+	}
+
+	if ( $plugin_file ) {
+		// Manually load the event plugin.
+		require_once $plugin_dir . $plugin_file;
+		$current   = get_option( 'active_plugins', array() );
+		$current[] = $plugin_file;
+		sort( $current );
+		update_option( 'active_plugins', $current );
+	}
+
+	// Hot fix that allows using Events Manager within unit tests, because the em_init() is later not run as admin.
+	if ( 'events_manager' === $activitypub_event_extension_integration_filter ) {
+		require_once $plugin_dir . 'events-manager/em-install.php';
+		em_create_events_table();
+		em_create_events_meta_table();
+		em_create_locations_table();
+	}
+
+	// At last manually load our WordPress plugin.
 	require dirname( __DIR__ ) . '/activitypub-event-extensions.php';
 }
 
diff --git a/tests/test-class-plugin-events-manger.php b/tests/test-class-plugin-events-manger.php
new file mode 100644
index 0000000..cf4bc46
--- /dev/null
+++ b/tests/test-class-plugin-events-manger.php
@@ -0,0 +1,184 @@
+<?php
+/**
+ * Class SampleTest
+ *
+ * @package Activitypub_Event_Extensions
+ */
+
+/**
+ * Sample test case.
+ */
+class Test_Events_Manager extends WP_UnitTestCase {
+	/**
+	 * Override the setup function, so that tests don't run if the Events Calendar is not active.
+	 */
+	public function set_up() {
+		parent::set_up();
+
+		if ( ! class_exists( 'EM_Events' ) ) {
+			self::markTestSkipped( 'VS Event List plugin is not active.' );
+		}
+
+		// For tests allow every user to create new events.
+		update_option( 'dbem_events_anonymous_submissions', true );
+
+		// Make sure that ActivityPub support is enabled for Events Manager.
+		$aec = \Activitypub_Event_Extensions\Setup::get_instance();
+		$aec->activate_activitypub_support_for_active_event_plugins();
+
+		// Delete all posts afterwards.
+		_delete_all_posts();
+	}
+
+	/**
+	 * Test that the right transformer gets applied.
+	 */
+	public function test_transformer_class() {
+		// We only test for one event plugin being active at the same time,
+		// even though we support multiple onces in theory.
+		// But testing all combinations is beyond scope.
+		$active_event_plugins = \Activitypub_Event_Extensions\Setup::get_instance()->get_active_event_plugins();
+		$this->assertEquals( 1, count( $active_event_plugins ) );
+
+		// Enable ActivityPub support for the event plugin.
+		$this->assertContains( EM_POST_TYPE_EVENT, get_option( 'activitypub_support_post_types' ) );
+
+		// Insert a new Event.
+		$wp_post_id = wp_insert_post(
+			array(
+				'post_title'  => 'Events Manager Test event',
+				'post_status' => 'published',
+				'post_type'   => EM_POST_TYPE_EVENT,
+				'meta_input'  => array(
+					'event_start_time' => strtotime( '+10 days 15:00:00' ),
+				),
+			)
+		);
+
+		$wp_object = get_post( $wp_post_id );
+
+		// Call the transformer Factory.
+		$transformer = \Activitypub\Transformer\Factory::get_transformer( $wp_object );
+
+		// Check that we got the right transformer.
+		$this->assertInstanceOf( \Activitypub_Event_Extensions\Activitypub\Transformer\Events_Manager::class, $transformer );
+	}
+
+	/**
+	 * Test the transformation of a minimal event.
+	 */
+	public function test_transform_of_minimal_event() {
+		// Create mockup event.
+		$event                   = new EM_Event();
+		$event->event_name       = 'Events Manager Test event';
+		$event->post_content     = 'Event description';
+		$event->event_start_date = gmdate( 'Y-m-d', strtotime( '+10 days 15:00:00' ) );
+		$event->event_start_time = '15:00:00';
+		$event->start            = strtotime( $event->event_start_date . ' ' . $event->event_start_time );
+		$event->force_status     = 'published';
+		$event->event_rsvp       = false;
+		$this->assertTrue( $event->save() );
+
+		// Call the transformer Factory.
+		$event_array = \Activitypub\Transformer\Factory::get_transformer( get_post( $event->post_id ) )->to_object()->to_array();
+
+		// Check that we got the right transformer.
+		$this->assertEquals( 'Event', $event_array['type'] );
+		$this->assertEquals( 'Events Manager Test event', $event_array['name'] );
+		$this->assertEquals( '', $event_array['content'] );
+		$this->assertEquals( gmdate( 'Y-m-d', strtotime( '+10 days 15:00:00' ) ) . 'T15:00:00Z', $event_array['startTime'] );
+		$this->assertEquals( comments_open( $event->post_id ), $event_array['commentsEnabled'] );
+		$this->assertEquals( comments_open( $event->post_id ) ? 'allow_all' : 'closed', $event_array['repliesModerationOption'] );
+		$this->assertEquals( 'external', $event_array['joinMode'] );
+		$this->assertArrayNotHasKey( 'location', $event_array );
+		$this->assertArrayNotHasKey( 'endTime', $event_array );
+		$this->assertEquals( 'MEETING', $event_array['category'] );
+	}
+
+	/**
+	 * Test the transformation of a event with full location.
+	 */
+	public function test_transform_of__full_event_with_location() {
+		// Create a mockup location.
+		$location                    = new EM_Location();
+		$location->location_name     = 'Test location';
+		$location->location_address  = 'Test Address';
+		$location->location_town     = 'Test Town';
+		$location->location_state    = 'Test state';
+		$location->location_postcode = '1337';
+		$location->location_region   = 'Test region';
+		$location->location_country  = 'AT'; // Must be a two char country code.
+		$this->assertTrue( $location->save() );
+
+		// Create mockup event.
+		$event                   = new EM_Event();
+		$event->event_name       = 'Events Manager Test event';
+		$event->post_content     = 'Event description';
+		$event->location_id      = $location->location_id;
+		$event->event_start_date = gmdate( 'Y-m-d', strtotime( '+10 days 15:00:00' ) );
+		$event->event_end_date   = gmdate( 'Y-m-d', strtotime( '+10 days 16:00:00' ) );
+		$event->event_start_time = '15:00:00';
+		$event->event_end_time   = '16:00:00';
+		$event->start            = strtotime( $event->event_start_date . ' ' . $event->event_start_time );
+		$event->end              = strtotime( $event->event_end_date . ' ' . $event->event_end_time );
+		$event->force_status     = 'published';
+		$event->event_rsvp       = false;
+		$this->assertTrue( $event->save() );
+
+		// Call the transformer Factory.
+		$event_array = \Activitypub\Transformer\Factory::get_transformer( get_post( $event->post_id ) )->to_object()->to_array();
+
+		// Check that we got the right transformer.
+		$this->assertEquals( 'Event', $event_array['type'] );
+		$this->assertEquals( 'Events Manager Test event', $event_array['name'] );
+		$this->assertEquals( '', $event_array['content'] );
+		$this->assertEquals( gmdate( 'Y-m-d', strtotime( '+10 days 15:00:00' ) ) . 'T15:00:00Z', $event_array['startTime'] );
+		$this->assertEquals( 'external', $event_array['joinMode'] );
+		$this->assertEquals( 'MEETING', $event_array['category'] );
+		$this->assertArrayHasKey( 'location', $event_array );
+		$this->assertEquals( 'Test location', $event_array['location']['name'] );
+		$this->assertEquals( 'Test Address', $event_array['location']['address']['postalAddress'] );
+		$this->assertEquals( 'Test Town', $event_array['location']['address']['addressLocality'] );
+		$this->assertEquals( 'Test state', $event_array['location']['address']['addressRegion'] );
+		$this->assertEquals( '1337', $event_array['location']['address']['postalCode'] );
+		$this->assertEquals( 'AT', $event_array['location']['address']['addressCountry'] );
+	}
+
+	/**
+	 * Test the transformation of a minimal event.
+	 */
+	public function test_transform_of_event_with_name_only_location() {
+		// Create a mockup location.
+		$location                = new EM_Location();
+		$location->location_name = 'Name only location';
+		$this->assertTrue( $location->save() );
+
+		// Create mockup event.
+		$event                   = new EM_Event();
+		$event->event_name       = 'Events Manager Test event';
+		$event->post_content     = 'Event description';
+		$event->location_id      = $location->location_id;
+		$event->event_start_date = gmdate( 'Y-m-d', strtotime( '+10 days 15:00:00' ) );
+		$event->event_end_date   = gmdate( 'Y-m-d', strtotime( '+10 days 16:00:00' ) );
+		$event->event_start_time = '15:00:00';
+		$event->event_end_time   = '16:00:00';
+		$event->start            = strtotime( $event->event_start_date . ' ' . $event->event_start_time );
+		$event->end              = strtotime( $event->event_end_date . ' ' . $event->event_end_time );
+		$event->force_status     = 'published';
+		$event->event_rsvp       = false;
+		$this->assertTrue( $event->save() );
+
+		// Call the transformer Factory.
+		$event_array = \Activitypub\Transformer\Factory::get_transformer( get_post( $event->post_id ) )->to_object()->to_array();
+
+		// Check that we got the right transformer.
+		$this->assertEquals( 'Event', $event_array['type'] );
+		$this->assertEquals( 'Events Manager Test event', $event_array['name'] );
+		$this->assertEquals( '', $event_array['content'] );
+		$this->assertEquals( gmdate( 'Y-m-d', strtotime( '+10 days 15:00:00' ) ) . 'T15:00:00Z', $event_array['startTime'] );
+		$this->assertEquals( 'external', $event_array['joinMode'] );
+		$this->assertEquals( 'MEETING', $event_array['category'] );
+		$this->assertArrayHasKey( 'location', $event_array );
+		$this->assertEquals( 'Name only location', $event_array['location']['name'] );
+	}
+}
diff --git a/tests/test-class-plugin-gatherpress.php b/tests/test-class-plugin-gatherpress.php
new file mode 100644
index 0000000..504dc9c
--- /dev/null
+++ b/tests/test-class-plugin-gatherpress.php
@@ -0,0 +1,103 @@
+<?php
+/**
+ * Class SampleTest
+ *
+ * @package Activitypub_Event_Extensions
+ */
+
+/**
+ * Sample test case.
+ */
+class Test_GatherPress extends WP_UnitTestCase {
+	/**
+	 * Override the setup function, so that tests don't run if the Events Calendar is not active.
+	 */
+	public function set_up() {
+		parent::set_up();
+
+		if ( ! defined( 'GATHERPRESS_CORE_FILE' ) ) {
+			self::markTestSkipped( 'GatherPress plugin is not active.' );
+		}
+
+		// Mock the plugin activation.
+		GatherPress\Core\Setup::get_instance()->activate_gatherpress_plugin( false );
+
+		// Make sure that ActivityPub support is enabled for The Events Calendar.
+		$aec = \Activitypub_Event_Extensions\Setup::get_instance();
+		$aec->activate_activitypub_support_for_active_event_plugins();
+
+		// Delete all posts afterwards.
+		_delete_all_posts();
+	}
+
+	/**
+	 * Test that the right transformer gets applied.
+	 */
+	public function test_transformer_class() {
+		// We only test for one event plugin being active at the same time,
+		// even though we support multiple onces in theory.
+		// But testing all combinations is beyond scope.
+		$active_event_plugins = \Activitypub_Event_Extensions\Setup::get_instance()->get_active_event_plugins();
+		$this->assertEquals( 1, count( $active_event_plugins ) );
+
+		// Enable ActivityPub support for the event plugin.
+		$this->assertContains( 'gatherpress_event', get_option( 'activitypub_support_post_types' ) );
+
+		// Mock GatherPress Event.
+		$post_id = wp_insert_post(
+			array(
+				'post_title'   => 'Unit Test Event',
+				'post_type'    => 'gatherpress_event',
+				'post_content' => 'Unit Test description.',
+			)
+		);
+		$event   = new \GatherPress\Core\Event( $post_id );
+		$params  = array(
+			'datetime_start' => '+10 days 15:00:00',
+			'datetime_end'   => '+10 days 16:00:00',
+			'timezone'       => 'America/New_York',
+		);
+
+		$event->save_datetimes( $params );
+
+		// Call the transformer Factory.
+		$transformer = \Activitypub\Transformer\Factory::get_transformer( $event->event );
+
+		// Check that we got the right transformer.
+		$this->assertInstanceOf( \Activitypub_Event_Extensions\Activitypub\Transformer\GatherPress::class, $transformer );
+	}
+
+	/**
+	 * Test transformation to ActivityPUb for basic event.
+	 */
+	public function test_transform_of_basic_event() {
+		// Mock GatherPress Event.
+		$post_id = wp_insert_post(
+			array(
+				'post_title'   => 'Unit Test Event',
+				'post_type'    => 'gatherpress_event',
+				'post_content' => 'Unit Test description.',
+				'post_status'  => 'published',
+			)
+		);
+		$event   = new \GatherPress\Core\Event( $post_id );
+		$params  = array(
+			'datetime_start' => '+10 days 15:00:00',
+			'datetime_end'   => '+10 days 16:00:00',
+			'timezone'       => 'America/New_York',
+		);
+		$event->save_datetimes( $params );
+
+		// Call the transformer Factory.
+		$event_array = \Activitypub\Transformer\Factory::get_transformer( $event->event )->to_object()->to_array();
+
+		// Check that the event ActivityStreams representation contains everything as expected.
+		$this->assertEquals( 'Event', $event_array['type'] );
+		$this->assertEquals( 'Unit Test Event', $event_array['name'] );
+		$this->assertEquals( 'Unit Test description.', $event_array['content'] );
+		$this->assertEquals( gmdate( 'Y-m-d', strtotime( '+10 days 15:00:00' ) ) . 'T15:00:00Z', $event_array['startTime'] );
+		$this->assertEquals( gmdate( 'Y-m-d', strtotime( '+10 days 16:00:00' ) ) . 'T16:00:00Z', $event_array['endTime'] );
+		$this->assertEquals( 'external', $event_array['joinMode'] );
+		$this->assertArrayNotHasKey( 'location', $event_array );
+	}
+}
diff --git a/tests/test-class-plugin-the-events-calendar.php b/tests/test-class-plugin-the-events-calendar.php
index 3f161f7..c4f5f6d 100644
--- a/tests/test-class-plugin-the-events-calendar.php
+++ b/tests/test-class-plugin-the-events-calendar.php
@@ -72,7 +72,7 @@ class Test_The_Events_Calendar extends WP_UnitTestCase {
 	/**
 	 * Test that the right transformer gets applied.
 	 */
-	public function test_transformer_class() {
+	public function test_the_events_calendar_transformer_class() {
 		// We only test for one event plugin being active at the same time,
 		// even though we support multiple onces in theory.
 		// But testing all combinations is beyond scope.
@@ -180,7 +180,7 @@ class Test_The_Events_Calendar extends WP_UnitTestCase {
 	}
 
 	/**
-	 * Test transformation of  minimal event with minimal venue.
+	 * Test transformation of  minimal event with fully filled venue.
 	 */
 	public function test_transform_of_minimal_event_with_address_venue() {
 		// Create Venue.
diff --git a/tests/test-class-plugin-vs-event-list.php b/tests/test-class-plugin-vs-event-list.php
new file mode 100644
index 0000000..98d5830
--- /dev/null
+++ b/tests/test-class-plugin-vs-event-list.php
@@ -0,0 +1,211 @@
+<?php
+/**
+ * Class SampleTest
+ *
+ * @package Activitypub_Event_Extensions
+ */
+
+/**
+ * Sample test case.
+ */
+class Test_VS_Event_List extends WP_UnitTestCase {
+	/**
+	 * Override the setup function, so that tests don't run if the Events Calendar is not active.
+	 */
+	public function set_up() {
+		parent::set_up();
+
+		if ( ! function_exists( 'vsel_custom_post_type' ) ) {
+			self::markTestSkipped( 'VS Event List plugin is not active.' );
+		}
+
+		// Make sure that ActivityPub support is enabled for The Events Calendar.
+		$aec = \Activitypub_Event_Extensions\Setup::get_instance();
+		$aec->activate_activitypub_support_for_active_event_plugins();
+
+		// Delete all posts afterwards.
+		_delete_all_posts();
+	}
+
+	/**
+	 * Test that the right transformer gets applied.
+	 */
+	public function test_transformer_class() {
+		// We only test for one event plugin being active at the same time,
+		// even though we support multiple onces in theory.
+		// But testing all combinations is beyond scope.
+		$active_event_plugins = \Activitypub_Event_Extensions\Setup::get_instance()->get_active_event_plugins();
+		$this->assertEquals( 1, count( $active_event_plugins ) );
+
+		// Enable ActivityPub support for the event plugin.
+		$this->assertContains( 'event', get_option( 'activitypub_support_post_types' ) );
+
+		// Insert a new Event.
+		$wp_post_id = wp_insert_post(
+			array(
+				'post_title'  => 'VSEL Test Event',
+				'post_status' => 'published',
+				'post_type'   => 'event',
+				'meta_input'  => array(
+					'event-start-date' => strtotime( '+10 days 15:00:00' ),
+				),
+			)
+		);
+
+		$wp_object = get_post( $wp_post_id );
+
+		// Call the transformer Factory.
+		$transformer = \Activitypub\Transformer\Factory::get_transformer( $wp_object );
+
+		// Check that we got the right transformer.
+		$this->assertInstanceOf( \Activitypub_Event_Extensions\Activitypub\Transformer\VS_Event_List::class, $transformer );
+	}
+
+	/**
+	 * Test the transformation to ActivityStreams of minimal event.
+	 */
+	public function test_transform_of_minimal_event() {
+		// Insert a new Event.
+		$wp_post_id = wp_insert_post(
+			array(
+				'post_title'  => 'VSEL Test Event',
+				'post_status' => 'published',
+				'post_type'   => 'event',
+				'meta_input'  => array(
+					'event-start-date' => strtotime( '+10 days 15:00:00' ),
+				),
+			)
+		);
+
+		// Transform the event to ActivityStreams.
+		$event_array = \Activitypub\Transformer\Factory::get_transformer( get_post( $wp_post_id ) )->to_object()->to_array();
+
+		// Check that the event ActivityStreams representation contains everything as expected.
+		$this->assertEquals( 'Event', $event_array['type'] );
+		$this->assertEquals( 'VSEL Test Event', $event_array['name'] );
+		$this->assertEquals( '', $event_array['content'] );
+		$this->assertEquals( gmdate( 'Y-m-d', strtotime( '+10 days 15:00:00' ) ) . 'T15:00:00Z', $event_array['startTime'] );
+		$this->assertArrayNotHasKey( 'endTime', $event_array );
+		$this->assertEquals( comments_open( $wp_post_id ), $event_array['commentsEnabled'] );
+		$this->assertEquals( comments_open( $wp_post_id ) ? 'allow_all' : 'closed', $event_array['repliesModerationOption'] );
+		$this->assertEquals( 'external', $event_array['joinMode'] );
+		$this->assertEquals( esc_url( get_permalink( $wp_post_id ) ), $event_array['externalParticipationUrl'] );
+		$this->assertArrayNotHasKey( 'location', $event_array );
+		$this->assertEquals( 'MEETING', $event_array['category'] );
+	}
+
+	/**
+	 * Test the transformation to ActivityStreams of minimal event.
+	 */
+	public function test_transform_of_full_event() {
+		// Insert a new Event.
+		$wp_post_id = wp_insert_post(
+			array(
+				'post_title'  => 'VSEL Test Event',
+				'post_status' => 'published',
+				'post_type'   => 'event',
+				'meta_input'  => array(
+					'event-start-date' => strtotime( '+10 days 15:00:00' ),
+					'event-date'       => strtotime( '+10 days 16:00:00' ),
+					'event-link'       => 'https://event-federation.eu/vsel-test-event',
+					'event-link-label' => 'Website',
+				),
+			)
+		);
+
+		// Transform the event to ActivityStreams.
+		$event_array = \Activitypub\Transformer\Factory::get_transformer( get_post( $wp_post_id ) )->to_object()->to_array();
+
+		// Check that the event ActivityStreams representation contains everything as expected.
+		$this->assertEquals( 'Event', $event_array['type'] );
+		$this->assertEquals( 'VSEL Test Event', $event_array['name'] );
+		$this->assertEquals( '', $event_array['content'] );
+		$this->assertEquals( gmdate( 'Y-m-d', strtotime( '+10 days 15:00:00' ) ) . 'T15:00:00Z', $event_array['startTime'] );
+		$this->assertEquals( gmdate( 'Y-m-d', strtotime( '+10 days 15:00:00' ) ) . 'T16:00:00Z', $event_array['endTime'] );
+		$this->assertEquals( comments_open( $wp_post_id ), $event_array['commentsEnabled'] );
+		$this->assertEquals( comments_open( $wp_post_id ) ? 'allow_all' : 'closed', $event_array['repliesModerationOption'] );
+		$this->assertEquals( 'external', $event_array['joinMode'] );
+		$this->assertEquals( esc_url( get_permalink( $wp_post_id ) ), $event_array['externalParticipationUrl'] );
+		$this->assertArrayNotHasKey( 'location', $event_array );
+		$this->assertEquals( 'MEETING', $event_array['category'] );
+		$this->assertContains(
+			array(
+				'type'      => 'Link',
+				'name'      => 'Website',
+				'href'      => 'https://event-federation.eu/vsel-test-event',
+				'mediaType' => 'text/html',
+			),
+			$event_array['attachment']
+		);
+	}
+
+	/**
+	 * Test the transformation to ActivityStreams of event with hidden end time.
+	 */
+	public function test_transform_of_event_with_hidden_end_time() {
+		// Insert a new Event.
+		$wp_post_id = wp_insert_post(
+			array(
+				'post_title'  => 'VSEL Test Event',
+				'post_status' => 'published',
+				'post_type'   => 'event',
+				'meta_input'  => array(
+					'event-start-date'    => strtotime( '+10 days 15:00:00' ),
+					'event-date'          => strtotime( '+10 days 16:00:00' ),
+					'event-hide-end-time' => 'yes',
+				),
+			)
+		);
+
+		// Transform the event to ActivityStreams.
+		$event_array = \Activitypub\Transformer\Factory::get_transformer( get_post( $wp_post_id ) )->to_object()->to_array();
+
+		// Check that the event ActivityStreams representation contains everything as expected.
+		$this->assertArrayNotHasKey( 'endTime', $event_array );
+	}
+
+	/**
+	 * Test transformation of event with mapped category.
+	 */
+	public function test_transform_event_with_mapped_categories() {
+		// Create category.
+		$category_id_music   = wp_insert_term( 'Music', 'event_cat', array( 'slug' => 'music' ) );
+		$category_id_theatre = wp_insert_term( 'Theatre', 'event_cat', array( 'slug' => 'theatre' ) );
+
+		// Set default mapping for event categories.
+		update_option( 'activitypub_event_extensions_default_event_category', 'MUSIC' );
+
+		// Set an override for the category with the slug theatre.
+		update_option( 'activitypub_event_extensions_event_category_mappings', array( 'theatre' => 'THEATRE' ) );
+
+		// Create a VS Event List event with the music category.
+		$wp_post_id = wp_insert_post(
+			array(
+				'post_title'  => 'VSEL Test Event',
+				'post_status' => 'published',
+				'post_type'   => 'event',
+				'meta_input'  => array(
+					'event-start-date'    => strtotime( '+10 days 15:00:00' ),
+					'event-date'          => strtotime( '+10 days 16:00:00' ),
+					'event-hide-end-time' => 'yes',
+				),
+			)
+		);
+		wp_set_post_terms( $wp_post_id, $category_id_music['term_id'], 'event_cat' );
+
+		// Call the transformer.
+		$event_array = \Activitypub\Transformer\Factory::get_transformer( get_post( $wp_post_id ) )->to_object()->to_array();
+
+		// See if the default category mapping is applied.
+		$this->assertEquals( 'MUSIC', $event_array['category'] );
+
+		// Change the event category to theatre.
+		wp_set_post_terms( $wp_post_id, $category_id_theatre['term_id'], 'event_cat', false );
+
+		// Call the transformer.
+		$event_array = \Activitypub\Transformer\Factory::get_transformer( get_post( $wp_post_id ) )->to_object()->to_array();
+
+		// See if the default category mapping is applied.
+		$this->assertEquals( 'THEATRE', $event_array['category'] );
+	}
+}