diff --git a/src/WP_Queue/Connections/DatabaseConnection.php b/src/WP_Queue/Connections/DatabaseConnection.php
index 3607feb..6f3b61d 100644
--- a/src/WP_Queue/Connections/DatabaseConnection.php
+++ b/src/WP_Queue/Connections/DatabaseConnection.php
@@ -89,30 +89,43 @@ public function pop() {
 	 * Delete a job from the queue.
 	 *
 	 * @param Job $job
+	 *
+	 * @return bool
 	 */
 	public function delete( $job ) {
 		$where = array(
 			'id' => $job->id(),
 		);
 
-		$this->database->delete( $this->jobs_table, $where );
+		if ( $this->database->delete( $this->jobs_table, $where ) ) {
+			return true;
+		}
+
+		return false;
 	}
 
 	/**
 	 * Release a job back onto the queue.
 	 *
 	 * @param Job $job
+	 *
+	 * @return bool
 	 */
 	public function release( $job ) {
-		$data = array(
+		$data  = array(
 			'job'         => serialize( $job ),
 			'attempts'    => $job->attempts(),
 			'reserved_at' => null,
 		);
-
-		$this->database->update( $this->jobs_table, $data, array(
+		$where = array(
 			'id' => $job->id(),
-		) );
+		);
+
+		if ( $this->database->update( $this->jobs_table, $data, $where ) ) {
+			return true;
+		}
+
+		return false;
 	}
 
 	/**
@@ -120,15 +133,23 @@ public function release( $job ) {
 	 *
 	 * @param Job       $job
 	 * @param Exception $exception
+	 *
+	 * @return bool
 	 */
 	public function failure( $job, Exception $exception ) {
-		$this->database->insert( $this->failures_table, array(
+		$insert = $this->database->insert( $this->failures_table, array(
 			'job'       => serialize( $job ),
 			'error'     => $this->format_exception( $exception ),
 			'failed_at' => $this->datetime(),
 		) );
 
-		$this->delete( $job );
+		if ( $insert ) {
+			$this->delete( $job );
+
+			return true;
+		}
+
+		return false;
 	}
 
 	/**
@@ -194,7 +215,7 @@ protected function vitalize_job( $raw_job ) {
 
 		$job->set_id( $raw_job->id );
 		$job->set_attempts( $raw_job->attempts );
-		$job->set_reserved_at( new Carbon( $raw_job->reserved_at ) );
+		$job->set_reserved_at( empty( $raw_job->reserved_at ) ? null : new Carbon( $raw_job->reserved_at ) );
 		$job->set_available_at( new Carbon( $raw_job->available_at ) );
 		$job->set_created_at( new Carbon( $raw_job->created_at ) );
 
diff --git a/src/WP_Queue/Job.php b/src/WP_Queue/Job.php
index d10e7fe..e160b56 100644
--- a/src/WP_Queue/Job.php
+++ b/src/WP_Queue/Job.php
@@ -95,9 +95,9 @@ public function reserved_at() {
 	/**
 	 * Set reserved at date.
 	 *
-	 * @param Carbon $reserved_at
+	 * @param null|Carbon $reserved_at
 	 */
-	public function set_reserved_at( Carbon $reserved_at ) {
+	public function set_reserved_at( $reserved_at ) {
 		$this->reserved_at = $reserved_at;
 	}
 
diff --git a/tests/TestDatabaseConnection.php b/tests/TestDatabaseConnection.php
new file mode 100644
index 0000000..35cfb3e
--- /dev/null
+++ b/tests/TestDatabaseConnection.php
@@ -0,0 +1,137 @@
+<?php
+
+use Carbon\Carbon;
+use PHPUnit\Framework\TestCase;
+use WP_Queue\Connections\DatabaseConnection;
+use WP_Queue\Job;
+
+class TestDatabaseConnection extends TestCase {
+
+	protected $wpdb;
+
+	public function setUp() {
+		WP_Mock::setUp();
+
+		$this->wpdb = Mockery::spy( 'WPDB' );;
+		$this->wpdb->prefix = "wp_";
+	}
+
+	public function tearDown() {
+		WP_Mock::tearDown();
+	}
+
+	public function test_push_success() {
+		$insert_id = 12345;
+		$this->wpdb->shouldReceive( 'insert' )->once()->andReturn( 1 );
+		$this->wpdb->insert_id = $insert_id;
+
+		$instance = new DatabaseConnection( $this->wpdb );
+
+		$this->assertEquals( $insert_id, $instance->push( new TestJob() ) );
+	}
+
+	public function test_push_fail() {
+		$this->wpdb->shouldReceive( 'insert' )->once()->andReturn( false );
+
+		$instance = new DatabaseConnection( $this->wpdb );
+
+		$this->assertFalse( $instance->push( new TestJob() ) );
+	}
+
+	public function test_pop_success() {
+		$this->wpdb->shouldReceive( 'get_row' )->once()->andReturn( (object) array(
+			'id'           => 12345,
+			'job'          => serialize( new TestJob() ),
+			'attempts'     => 0,
+			'reserved_at'  => null,
+			'available_at' => '2017-10-09 00:00:00',
+			'created_at'   => '2017-10-09 00:00:00',
+		) );
+		$instance = new DatabaseConnection( $this->wpdb );
+		$job = $instance->pop();
+
+		$this->assertInstanceOf( TestJob::class, $job );
+		$this->assertEquals( 12345, $job->id() );
+		$this->assertEquals( 0, $job->attempts() );
+		$this->assertNull( $job->reserved_at() );
+		$this->assertInstanceOf( Carbon::class, $job->available_at() );
+		$this->assertInstanceOf( Carbon::class, $job->created_at() );
+	}
+
+	public function test_pop_fail() {
+		$this->wpdb->shouldReceive( 'get_row' )->once()->andReturn( null );
+		$instance = new DatabaseConnection( $this->wpdb );
+
+		$this->assertFalse( $instance->pop() );
+	}
+
+	public function test_delete_success() {
+		$this->wpdb->shouldReceive( 'delete' )->once()->andReturn( 1 );
+
+		$instance = new DatabaseConnection( $this->wpdb );
+
+		$this->assertTrue( $instance->delete( new TestJob() ) );
+	}
+
+	public function test_delete_fail() {
+		$this->wpdb->shouldReceive( 'delete' )->once()->andReturn( false );
+
+		$instance = new DatabaseConnection( $this->wpdb );
+
+		$this->assertFalse( $instance->delete( new TestJob() ) );
+	}
+
+	public function test_release_success() {
+		$this->wpdb->shouldReceive( 'update' )->once()->andReturn( 1 );
+
+		$instance = new DatabaseConnection( $this->wpdb );
+
+		$this->assertTrue( $instance->release( new TestJob() ) );
+	}
+
+	public function test_release_fail() {
+		$this->wpdb->shouldReceive( 'update' )->once()->andReturn( false );
+
+		$instance = new DatabaseConnection( $this->wpdb );
+
+		$this->assertFalse( $instance->release( new TestJob() ) );
+	}
+
+	public function test_failure_success() {
+		$this->wpdb->shouldReceive( 'insert' )->once()->andReturn( 1 );
+
+		$instance = new DatabaseConnection( $this->wpdb );
+
+		$this->assertTrue( $instance->failure( new TestJob(), new Exception() ) );
+	}
+
+	public function test_failure_fail() {
+		$this->wpdb->shouldReceive( 'insert' )->once()->andReturn( false );
+
+		$instance = new DatabaseConnection( $this->wpdb );
+
+		$this->assertFalse( $instance->failure( new TestJob(), new Exception() ) );
+	}
+
+	public function test_jobs() {
+		$count = rand( 1, 100 );
+		$this->wpdb->shouldReceive( 'get_var' )->once()->andReturn( $count );
+
+		$instance = new DatabaseConnection( $this->wpdb );
+
+		$this->assertEquals( $count, $instance->jobs() );
+	}
+
+	public function test_failed_jobs() {
+		$count = rand( 1, 100 );
+		$this->wpdb->shouldReceive( 'get_var' )->once()->andReturn( $count );
+
+		$instance = new DatabaseConnection( $this->wpdb );
+
+		$this->assertEquals( $count, $instance->failed_jobs() );
+	}
+}
+
+class TestJob extends Job {
+	public function handle() {}
+}
\ No newline at end of file