diff --git a/lib/Activity/ActivityManager.php b/lib/Activity/ActivityManager.php
index f6e9de405..3dbcd5852 100644
--- a/lib/Activity/ActivityManager.php
+++ b/lib/Activity/ActivityManager.php
@@ -23,6 +23,7 @@
 
 namespace OCA\Deck\Activity;
 
+use InvalidArgumentException;
 use OCA\Deck\Db\AssignedUsers;
 use OCA\Deck\Db\Attachment;
 use OCA\Deck\Db\AttachmentMapper;
@@ -127,7 +128,7 @@ class ActivityManager {
 		$subject = '';
 		switch ($subjectIdentifier) {
 			case self::SUBJECT_BOARD_CREATE:
-				$subject = $this->l10n->t('You have created a new board {board}');
+				$subject = $ownActivity ? $this->l10n->t('You have created a new board {board}'): $this->l10n->t('{user} has created a new board {board}');
 				break;
 			case self::SUBJECT_BOARD_DELETE:
 				$subject = $ownActivity ? $this->l10n->t('You have deleted the board {board}') : $this->l10n->t('{user} has deleted the board {board}');
@@ -174,7 +175,7 @@ class ActivityManager {
 				$subject = $ownActivity ? $this->l10n->t('You have renamed the card {before} to {card}') : $this->l10n->t('{user} has renamed the card {before} to {card}');
 				break;
 			case self::SUBJECT_CARD_UPDATE_DESCRIPTION:
-				if ($subjectParams['before'] === null) {
+				if (!isset($subjectParams['before'])) {
 					$subject = $ownActivity ? $this->l10n->t('You have added a description to {card} in {stack} on {board}') : $this->l10n->t('{user} has added a description to {card} in {stack} on {board}');
 				} else {
 					$subject = $ownActivity ? $this->l10n->t('You have updated the description of {card} in {stack} on {board}') : $this->l10n->t('{user} has updated the description {card} in {stack} on {board}');
@@ -187,9 +188,9 @@ class ActivityManager {
 				$subject = $ownActivity ? $this->l10n->t('You have unarchived {card} in {stack} on {board}') : $this->l10n->t('{user} has unarchived {card} in {stack} on {board}');
 				break;
 			case self::SUBJECT_CARD_UPDATE_DUEDATE:
-				if ($subjectParams['after'] === null) {
+				if (!isset($subjectParams['after'])) {
 					$subject = $ownActivity ? $this->l10n->t('You have removed the due date of {card}') : $this->l10n->t('{user} has removed the due date of {card}');
-				} else if ($subjectParams['before'] === null && $subjectParams['after'] !== null) {
+				} else if (isset($subjectParams['before']) && !isset($subjectParams['after'])) {
 					$subject = $ownActivity ? $this->l10n->t('You have set the due date of {card} to {after}') : $this->l10n->t('{user} has set the due date of {card} to {after}');
 				} else {
 					$subject = $ownActivity ? $this->l10n->t('You have updated the due date of {card} to {after}') : $this->l10n->t('{user} has updated the due date of {card} to {after}');
@@ -400,28 +401,36 @@ class ActivityManager {
 	private function findObjectForEntity($objectType, $entity) {
 		$className = \get_class($entity);
 		$objectId = null;
-		switch ($className) {
-			case Board::class:
-			case Card::class:
-				$objectId = $entity->getId();
-				break;
-			case Attachment::class:
-			case Label::class:
-			case AssignedUsers::class:
-				$objectId = $entity->getCardId();
-				break;
-			case Stack::class:
-				$objectId = $entity->getBoardId();
-		}
-
 		if ($objectType === self::DECK_OBJECT_CARD) {
+			switch ($className) {
+				case Card::class:
+					$objectId = $entity->getId();
+					break;
+				case Attachment::class:
+				case Label::class:
+				case AssignedUsers::class:
+					$objectId = $entity->getCardId();
+					break;
+				default:
+					throw new InvalidArgumentException('No entity relation present for '. $className . ' to ' . $objectType);
+			}
 			return $this->cardMapper->find($objectId);
 		}
 		if ($objectType === self::DECK_OBJECT_BOARD) {
+			switch ($className) {
+				case Board::class:
+					$objectId = $entity->getId();
+					break;
+				case Label::class:
+				case Stack::class:
+					$objectId = $entity->getBoardId();
+					break;
+				default:
+					throw new InvalidArgumentException('No entity relation present for '. $className . ' to ' . $objectType);
+			}
 			return $this->boardMapper->find($objectId);
 		}
-
-		return null;
+		throw new InvalidArgumentException('No entity relation present for '. $className . ' to ' . $objectType);
 	}
 
 	private function findDetailsForStack($stackId) {
diff --git a/tests/unit/Activity/ActivityManagerTest.php b/tests/unit/Activity/ActivityManagerTest.php
new file mode 100644
index 000000000..f5f3aa918
--- /dev/null
+++ b/tests/unit/Activity/ActivityManagerTest.php
@@ -0,0 +1,339 @@
+<?php
+/**
+ * @copyright Copyright (c) 2018 Julius Härtl <jus@bitgrid.net>
+ *
+ * @author Julius Härtl <jus@bitgrid.net>
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+namespace OCA\Deck\Activity;
+
+use OCA\Deck\Db\AssignedUsers;
+use OCA\Deck\Db\Attachment;
+use OCA\Deck\Db\AttachmentMapper;
+use OCA\Deck\Db\Board;
+use OCA\Deck\Db\BoardMapper;
+use OCA\Deck\Db\Card;
+use OCA\Deck\Db\CardMapper;
+use OCA\Deck\Db\Label;
+use OCA\Deck\Db\Stack;
+use OCA\Deck\Db\StackMapper;
+use OCA\Deck\Service\PermissionService;
+use OCP\Activity\IEvent;
+use OCP\Activity\IManager;
+use OCP\IL10N;
+use OCP\IUser;
+use PHPUnit\Framework\TestCase;
+use PHPUnit_Framework_MockObject_MockObject as MockObject;
+
+class ActivityManagerTest extends TestCase {
+
+	/** @var ActivityManager */
+	private $activityManager;
+	/** @var IManager|MockObject */
+	private $manager;
+	/** @var PermissionService|MockObject */
+	private $permissionService;
+	/** @var BoardMapper|MockObject */
+	private $boardMapper;
+	/** @var CardMapper|MockObject */
+	private $cardMapper;
+	/** @var StackMapper|MockObject */
+	private $stackMapper;
+	/** @var AttachmentMapper|MockObject */
+	private $attachmentMapper;
+	/** @var IL10N|MockObject */
+	private $l10n;
+	/** @var string */
+	private $userId = 'admin';
+
+	public function setUp() {
+		$this->manager = $this->createMock(IManager::class);
+		$this->permissionService = $this->createMock(PermissionService::class);
+		$this->boardMapper = $this->createMock(BoardMapper::class);
+		$this->cardMapper = $this->createMock(CardMapper::class);
+		$this->stackMapper = $this->createMock(StackMapper::class);
+		$this->attachmentMapper = $this->createMock(AttachmentMapper::class);
+		$this->l10n = $this->createMock(IL10N::class);
+		$this->activityManager = new ActivityManager(
+			$this->manager,
+			$this->permissionService,
+			$this->boardMapper,
+			$this->cardMapper,
+			$this->stackMapper,
+			$this->attachmentMapper,
+			$this->l10n,
+			$this->userId
+		);
+	}
+
+	public function testGetActivityFormatOwn() {
+		$managerClass = new \ReflectionClass(ActivityManager::class);
+		$this->l10n->expects($this->any())
+			->method('t')
+			->will($this->returnCallback(function ($s) { return $s; }));
+
+		foreach ($managerClass->getConstants() as $constant => $value) {
+			if (strpos($constant, 'SUBJECT') === 0) {
+				$format = $this->activityManager->getActivityFormat($value, [], false);
+				if ($format !== '') {
+					$this->assertContains('{user}', $format);
+				} else {
+					/** @noinspection ForgottenDebugOutputInspection */
+					print_r('No activity string found for '. $constant . PHP_EOL);
+				}
+				$format = $this->activityManager->getActivityFormat($value, [], true);
+				if ($format !== '') {
+					$this->assertStringStartsWith('You', $format);
+				} else {
+					/** @noinspection ForgottenDebugOutputInspection */
+					print_r('No own activity string found for '. $constant . PHP_EOL);
+				}
+			}
+		}
+
+	}
+
+	public function testCreateEvent() {
+		$board = new Board();
+		$this->boardMapper->expects($this->once())
+			->method('find')
+			->willReturn($board);
+		$event = $this->createMock(IEvent::class);
+		$this->manager->expects($this->once())
+			->method('generateEvent')
+			->willReturn($event);
+		$event->expects($this->once())->method('setApp')->willReturn($event);
+		$event->expects($this->once())->method('setType')->willReturn($event);
+		$event->expects($this->once())->method('setAuthor')->willReturn($event);
+		$event->expects($this->once())->method('setObject')->willReturn($event);
+		$event->expects($this->once())->method('setSubject')->willReturn($event);
+		$event->expects($this->once())->method('setTimestamp')->willReturn($event);
+		$actual = $this->invokePrivate($this->activityManager, 'createEvent', [
+			ActivityManager::DECK_OBJECT_BOARD,
+			$board,
+			ActivityManager::SUBJECT_BOARD_CREATE
+		]);
+		$this->assertEquals($event, $actual);
+	}
+
+	public function dataSendToUsers() {
+		return [
+			[ActivityManager::DECK_OBJECT_BOARD],
+			[ActivityManager::DECK_OBJECT_CARD],
+		];
+	}
+
+	private function mockUser($uid) {
+		$user = $this->createMock(IUser::class);
+		$user->expects($this->any())
+			->method('getUID')
+			->willReturn($uid);
+		return $user;
+	}
+	/**
+	 * @dataProvider dataSendToUsers
+	 */
+	public function testSendToUser($objectType) {
+		$users = [
+			$this->mockUser('user1'),
+			$this->mockUser('user2'),
+		];
+		$event = $this->createMock(IEvent::class);
+		$event->expects($this->at(0))
+			->method('getObjectType')
+			->willReturn($objectType);
+		$event->expects($this->at(0))
+			->method('getObjectId')
+			->willReturn(1);
+		$event->expects($this->at(2))
+			->method('setAffectedUser')
+			->with('user1');
+		$event->expects($this->at(3))
+			->method('setAffectedUser')
+			->with('user2');
+		$mapper = null;
+		switch ($objectType) {
+			case ActivityManager::DECK_OBJECT_BOARD:
+				$mapper = $this->boardMapper;
+				break;
+			case ActivityManager::DECK_OBJECT_CARD:
+				$mapper = $this->cardMapper;
+				break;
+		}
+		$mapper->expects($this->once())
+			->method('findBoardId')
+			->willReturn(123);
+		$this->permissionService->expects($this->once())
+			->method('findUsers')
+			->willReturn($users);
+		$this->manager->expects($this->at(0))
+			->method('publish')
+			->with($event);
+		$this->manager->expects($this->at(1))
+			->method('publish')
+			->with($event);
+		$this->invokePrivate($this->activityManager, 'sendToUsers', [$event]);
+	}
+
+	public function dataFindObjectForEntity() {
+		$board = new Board();
+		$board->setId(1);
+		$stack = new Stack();
+		$stack->setBoardId(1);
+		$card = new Card();
+		$card->setId(3);
+		$attachment = new Attachment();
+		$attachment->setCardId(3);
+		$label = new Label();
+		$label->setCardId(3);
+		$label->setBoardId(1);
+		$assignedUser = new AssignedUsers();
+		$assignedUser->setCardId(3);
+
+		return [
+			[ActivityManager::DECK_OBJECT_BOARD, $board],
+			[ActivityManager::DECK_OBJECT_BOARD, $stack],
+			[ActivityManager::DECK_OBJECT_BOARD, $label],
+			[ActivityManager::DECK_OBJECT_CARD, $card],
+			[ActivityManager::DECK_OBJECT_CARD, $attachment],
+			[ActivityManager::DECK_OBJECT_CARD, $assignedUser],
+			[ActivityManager::DECK_OBJECT_CARD, $label],
+		];
+	}
+
+	/**
+	 * @param $objectType
+	 * @param $entity
+	 * @dataProvider dataFindObjectForEntity
+	 */
+	public function testFindObjectForEntity($objectType, $entity) {
+		$board = new Board();
+		$board->setId(1);
+		$card = new Card();
+		$card->setId(3);
+		$expected = null;
+		if ($objectType === ActivityManager::DECK_OBJECT_BOARD) {
+			$this->boardMapper->expects($this->once())
+				->method('find')
+				->with(1)
+				->willReturn($board);
+			$expected = $board;
+		}
+		if ($objectType === ActivityManager::DECK_OBJECT_CARD) {
+			$this->cardMapper->expects($this->once())
+				->method('find')
+				->with(3)
+				->willReturn($card);
+			$expected = $card;
+		}
+		$actual = $this->invokePrivate($this->activityManager, 'findObjectForEntity', [$objectType, $entity]);
+		$this->assertEquals($expected, $actual);
+	}
+
+	public function testFindDetailsForStack() {
+		$stack = new Stack();
+		$stack->setId(123);
+		$stack->setBoardId(999);
+		$board = new Board();
+		$board->setId(999);
+		$this->stackMapper->expects($this->once())
+			->method('find')
+			->with(123)
+			->willReturn($stack);
+		$this->boardMapper->expects($this->once())->method('find')
+			->with(999)
+			->willReturn($board);
+		$this->assertEquals([
+			'stack' => $stack,
+			'board' => $board
+		], $this->invokePrivate($this->activityManager, 'findDetailsForStack', [123]));
+	}
+
+
+	public function testFindDetailsForCard() {
+		$card = new Card();
+		$card->setId(555);
+		$card->setStackId(123);
+		$stack = new Stack();
+		$stack->setId(123);
+		$stack->setBoardId(999);
+		$board = new Board();
+		$board->setId(999);
+		$this->cardMapper->expects($this->once())
+			->method('find')
+			->with(555)
+			->willReturn($card);
+		$this->stackMapper->expects($this->once())
+			->method('find')
+			->with(123)
+			->willReturn($stack);
+		$this->boardMapper->expects($this->once())->method('find')
+			->with(999)
+			->willReturn($board);
+		$this->assertEquals([
+			'stack' => $stack,
+			'board' => $board,
+			'card' => $card
+		], $this->invokePrivate($this->activityManager, 'findDetailsForCard', [555]));
+	}
+
+	public function testFindDetailsForAttachment() {
+		$attachment = new Attachment();
+		$attachment->setId(777);
+		$attachment->setCardId(555);
+		$card = new Card();
+		$card->setId(555);
+		$card->setStackId(123);
+		$stack = new Stack();
+		$stack->setId(123);
+		$stack->setBoardId(999);
+		$board = new Board();
+		$board->setId(999);
+		$this->attachmentMapper->expects($this->once())
+			->method('find')
+			->with(777)
+			->willReturn($attachment);
+		$this->cardMapper->expects($this->once())
+			->method('find')
+			->with(555)
+			->willReturn($card);
+		$this->stackMapper->expects($this->once())
+			->method('find')
+			->with(123)
+			->willReturn($stack);
+		$this->boardMapper->expects($this->once())->method('find')
+			->with(999)
+			->willReturn($board);
+		$this->assertEquals([
+			'stack' => $stack,
+			'board' => $board,
+			'card' => $card,
+			'attachment' => $attachment
+		], $this->invokePrivate($this->activityManager, 'findDetailsForAttachment', [777]));
+	}
+
+	public function invokePrivate(&$object, $methodName, array $parameters = array())
+	{
+		$reflection = new \ReflectionClass(get_class($object));
+		$method = $reflection->getMethod($methodName);
+		$method->setAccessible(true);
+		return $method->invokeArgs($object, $parameters);
+	}
+
+}