diff --git a/src/UglyQueue.php b/src/UglyQueue.php
index a9e01ec..a3e6fb0 100644
--- a/src/UglyQueue.php
+++ b/src/UglyQueue.php
@@ -58,10 +58,17 @@ class UglyQueue
 
     /**
      * @param int $ttl Time to live in seconds
+     * @throws \InvalidArgumentException
      * @return bool
      */
     public function lock($ttl = 250)
     {
+        if (!is_int($ttl))
+            throw new \InvalidArgumentException('UglyQueue::lock - Argument 1 expected to be positive integer, "'.gettype($ttl).'" seen');
+
+        if ($ttl < 0)
+            throw new \InvalidArgumentException('UglyQueue::lock - Argument 1 expected to be positive integer, "'.$ttl.'" seen');
+
         $already_locked = $this->isLocked();
 
         // If there is no lock, currently
@@ -102,10 +109,14 @@ class UglyQueue
     }
 
     /**
+     * @throws \RuntimeException
      * @return bool
      */
     public function isLocked()
     {
+        if ($this->init === false)
+            throw new \RuntimeException('UglyQueue::isLocked - Must first initialize queue');
+
         // First check for lock file
         if (is_file($this->queueGroupDirPath.'queue.lock'))
         {
@@ -248,13 +259,13 @@ HTML;
 
         // If we don't have a lock, assume issue and move on.
         if ($this->haveLock === false)
-            return false;
+            throw new \RuntimeException('UglyQueue::addToQueue - You do not have a lock on this queue');
 
         if (!is_resource($this->_tmpHandle))
         {
             $this->_tmpHandle = fopen($this->queueGroupDirPath.'queue.tmp', 'w+');
             if ($this->_tmpHandle === false)
-                return false;
+                throw new \RuntimeException('UglyQueue::addToQueue - Unable to create "queue.tmp" file');
         }
 
         if (is_array($value) || $value instanceof \stdClass)
diff --git a/tests/UglyQueue/UglyQueueTest.php b/tests/UglyQueue/UglyQueueTest.php
index a21339d..5f9ce0a 100644
--- a/tests/UglyQueue/UglyQueueTest.php
+++ b/tests/UglyQueue/UglyQueueTest.php
@@ -122,6 +122,30 @@ class UglyQueueTest extends PHPUnit_Framework_TestCase
         $this->assertNull($queueGroupDir);
     }
 
+    /**
+     * @covers \DCarbone\UglyQueue::isLocked
+     * @uses \DCarbone\UglyQueue
+     * @depends testCanConstructUglyQueueWithValidParameter
+     * @expectedException \RuntimeException
+     * @param \DCarbone\UglyQueue $uglyQueue
+     */
+    public function testExceptionThrownWhenCallingIsLockedOnUninitializedQueue(\DCarbone\UglyQueue $uglyQueue)
+    {
+        $isLocked = $uglyQueue->isLocked();
+    }
+
+    /**
+     * @covers \DCarbone\UglyQueue::addToQueue
+     * @uses \DCarbone\UglyQueue
+     * @depends testCanConstructUglyQueueWithValidParameter
+     * @expectedException \RuntimeException
+     * @param \DCarbone\UglyQueue $uglyQueue
+     */
+    public function testExceptionThrownWhenTryingToAddItemsToUninitializedQueue(\DCarbone\UglyQueue $uglyQueue)
+    {
+        $addToQueue = $uglyQueue->addToQueue('test', 'value');
+    }
+
     /**
      * @covers \DCarbone\UglyQueue::initialize
      * @covers \DCarbone\UglyQueue::getInit
@@ -139,6 +163,18 @@ class UglyQueueTest extends PHPUnit_Framework_TestCase
         return $uglyQueue;
     }
 
+    /**
+     * @covers \DCarbone\UglyQueue::addToQueue
+     * @uses \DCarbone\UglyQueue
+     * @depends testCanConstructUglyQueueWithValidParameter
+     * @expectedException \RuntimeException
+     * @param \DCarbone\UglyQueue $uglyQueue
+     */
+    public function testExceptionThrownWhenTryingToAddItemsToQueueWithoutLock(\DCarbone\UglyQueue $uglyQueue)
+    {
+        $addToQueue = $uglyQueue->addToQueue('test', 'value');
+    }
+
     /**
      * @covers \DCarbone\UglyQueue::getInit
      * @uses \DCarbone\UglyQueue
@@ -177,11 +213,25 @@ class UglyQueueTest extends PHPUnit_Framework_TestCase
         $this->assertEquals('tasty-sandwich', $queueGroup);
     }
 
+    /**
+     * @covers \DCarbone\UglyQueue::isLocked
+     * @uses \DCarbone\UglyQueue
+     * @depends testCanInitializeNewUglyQueue
+     * @param \DCarbone\UglyQueue $uglyQueue
+     */
+    public function testIsLockedReturnsFalseBeforeLockingAfterInitialization(\DCarbone\UglyQueue $uglyQueue)
+    {
+        $isLocked = $uglyQueue->isLocked();
+
+        $this->assertFalse($isLocked);
+    }
+
     /**
      * @covers \DCarbone\UglyQueue::initialize
      * @covers \DCarbone\UglyQueue::__construct
      * @covers \DCarbone\UglyQueue::getInit
      * @uses \DCarbone\UglyQueue
+     * @return \DCarbone\UglyQueue
      */
     public function testCanInitializeExistingQueue()
     {
@@ -198,10 +248,37 @@ class UglyQueueTest extends PHPUnit_Framework_TestCase
         $uglyQueue->initialize('tasty-sandwich');
 
         $this->assertTrue($uglyQueue->getInit());
+
+        return $uglyQueue;
     }
 
     /**
      * @covers \DCarbone\UglyQueue::lock
+     * @uses \DCarbone\UglyQueue
+     * @depends testCanConstructUglyQueueWithValidParameter
+     * @expectedException \InvalidArgumentException
+     * @param \DCarbone\UglyQueue $uglyQueue
+     */
+    public function testExceptionThrownWhenPassingNonIntegerValueToLock(\DCarbone\UglyQueue $uglyQueue)
+    {
+        $uglyQueue->lock('7 billion');
+    }
+
+    /**
+     * @covers \DCarbone\UglyQueue::lock
+     * @uses \DCarbone\UglyQueue
+     * @depends testCanConstructUglyQueueWithValidParameter
+     * @expectedException \InvalidArgumentException
+     * @param \DCarbone\UglyQueue $uglyQueue
+     */
+    public function testExceptionThrownWhenPassingNegativeIntegerValueToLock(\DCarbone\UglyQueue $uglyQueue)
+    {
+        $uglyQueue->lock(-73);
+    }
+
+    /**
+     * @covers \DCarbone\UglyQueue::lock
+     * @covers \DCarbone\UglyQueue::isLocked
      * @covers \DCarbone\UglyQueue::createQueueLock
      * @uses \DCarbone\UglyQueue
      * @depends testCanInitializeNewUglyQueue
@@ -228,4 +305,110 @@ class UglyQueueTest extends PHPUnit_Framework_TestCase
         return $uglyQueue;
     }
 
+    /**
+     * @covers \DCarbone\UglyQueue::lock
+     * @covers \DCarbone\UglyQueue::isLocked
+     * @uses \DCarbone\UglyQueue
+     * @depends testCanInitializeExistingQueue
+     * @param \DCarbone\UglyQueue $uglyQueue
+     */
+    public function testCannotLockInitializedQueueThatIsAlreadyLocked(\DCarbone\UglyQueue $uglyQueue)
+    {
+        $lock = $uglyQueue->lock();
+
+        $this->assertFalse($lock);
+    }
+
+    /**
+     * @covers \DCarbone\UglyQueue::isLocked
+     * @uses \DCarbone\UglyQueue
+     * @depends testCanLockUglyQueueWithDefaultTTL
+     * @param \DCarbone\UglyQueue $uglyQueue
+     */
+    public function testIsLockedReturnsTrueAfterLockingInitializedQueue(\DCarbone\UglyQueue $uglyQueue)
+    {
+        $isLocked = $uglyQueue->isLocked();
+        $this->assertTrue($isLocked);
+    }
+
+    /**
+     * @covers \DCarbone\UglyQueue::unlock
+     * @uses \DCarbone\UglyQueue
+     * @uses \DCarbone\Helpers\FileHelper
+     * @depends testCanLockUglyQueueWithDefaultTTL
+     * @param \DCarbone\UglyQueue $uglyQueue
+     * @return \DCarbone\UglyQueue
+     */
+    public function testCanUnlockLockedQueue(\DCarbone\UglyQueue $uglyQueue)
+    {
+        $uglyQueue->unlock();
+
+        $queueGroupDir = $uglyQueue->getQueueGroupDirPath();
+
+        $this->assertFileNotExists($queueGroupDir.'queue.lock');
+
+        return $uglyQueue;
+    }
+
+    /**
+     * @covers \DCarbone\UglyQueue::isLocked
+     * @uses \DCarbone\UglyQueue
+     * @depends testCanUnlockLockedQueue
+     * @param \DCarbone\UglyQueue $uglyQueue
+     */
+    public function testIsLockedReturnsFalseAfterUnlockingQueue(\DCarbone\UglyQueue $uglyQueue)
+    {
+        $isLocked = $uglyQueue->isLocked();
+
+        $this->assertFalse($isLocked);
+    }
+
+    /**
+     * @covers \DCarbone\UglyQueue::lock
+     * @covers \DCarbone\UglyQueue::isLocked
+     * @uses \DCarbone\UglyQueue
+     * @uses \DCarbone\Helpers\FileHelper
+     * @depends testCanUnlockLockedQueue
+     * @param \DCarbone\UglyQueue $uglyQueue
+     */
+    public function testIsLockedReturnsFalseWithStaleQueueLockFile(\DCarbone\UglyQueue $uglyQueue)
+    {
+        $uglyQueue->lock(2);
+        $isLocked = $uglyQueue->isLocked();
+        $this->assertTrue($isLocked);
+
+        sleep(3);
+
+        $isLocked = $uglyQueue->isLocked();
+        $this->assertFalse($isLocked);
+    }
+
+    /**
+     * @covers \DCarbone\UglyQueue::lock
+     * @covers \DCarbone\UglyQueue::isLocked
+     * @covers \DCarbone\UglyQueue::getQueueGroupDirPath
+     * @uses \DCarbone\UglyQueue
+     * @depends testCanUnlockLockedQueue
+     * @param \DCarbone\UglyQueue $uglyQueue
+     * @return \DCarbone\UglyQueue
+     */
+    public function testCanLockQueueWithValidIntegerValue(\DCarbone\UglyQueue $uglyQueue)
+    {
+        $locked = $uglyQueue->lock(200);
+
+        $this->assertTrue($locked);
+
+        $queueDir = $uglyQueue->getQueueGroupDirPath();
+
+        $this->assertFileExists($queueDir.'queue.lock');
+
+        $decode = @json_decode(file_get_contents($queueDir.'queue.lock'));
+
+        $this->assertTrue((json_last_error() === JSON_ERROR_NONE));
+        $this->assertObjectHasAttribute('ttl', $decode);
+        $this->assertObjectHasAttribute('born', $decode);
+        $this->assertEquals(200, $decode->ttl);
+
+        return $uglyQueue;
+    }
 }
\ No newline at end of file