diff --git a/spec/ActivityProfileDocumentSpec.php b/spec/ActivityProfileDocumentSpec.php
index 3f7dcec..0154c57 100644
--- a/spec/ActivityProfileDocumentSpec.php
+++ b/spec/ActivityProfileDocumentSpec.php
@@ -35,11 +35,8 @@ function it_is_a_document()
 
     function its_data_can_be_read()
     {
-        $this->offsetExists('x')->shouldReturn(true);
         $this->offsetGet('x')->shouldReturn('foo');
-        $this->offsetExists('y')->shouldReturn(true);
         $this->offsetGet('y')->shouldReturn('bar');
-        $this->offsetExists('z')->shouldReturn(false);
     }
 
     function it_throws_exception_when_not_existing_data_is_being_read()
diff --git a/spec/AgentProfileDocumentSpec.php b/spec/AgentProfileDocumentSpec.php
index e8dd7e0..f52d3a0 100644
--- a/spec/AgentProfileDocumentSpec.php
+++ b/spec/AgentProfileDocumentSpec.php
@@ -36,11 +36,8 @@ function it_is_a_document()
 
     function its_data_can_be_read()
     {
-        $this->offsetExists('x')->shouldReturn(true);
         $this->offsetGet('x')->shouldReturn('foo');
-        $this->offsetExists('y')->shouldReturn(true);
         $this->offsetGet('y')->shouldReturn('bar');
-        $this->offsetExists('z')->shouldReturn(false);
     }
 
     function it_throws_exception_when_not_existing_data_is_being_read()
diff --git a/spec/ExtensionsSpec.php b/spec/ExtensionsSpec.php
index a8a1472..de9fc6c 100644
--- a/spec/ExtensionsSpec.php
+++ b/spec/ExtensionsSpec.php
@@ -27,16 +27,13 @@ function its_extensions_can_be_read()
         $extensions->attach(IRI::fromString('http://id.tincanapi.com/extension/starting-position'), 1);
         $this->beConstructedWith($extensions);
 
-        $this->offsetExists(IRI::fromString('http://id.tincanapi.com/extension/topic'))->shouldReturn(true);
         $this->offsetGet(IRI::fromString('http://id.tincanapi.com/extension/topic'))->shouldReturn('Conformance Testing');
 
-        $this->offsetExists(IRI::fromString('http://id.tincanapi.com/extension/color'))->shouldReturn(true);
         $this->offsetGet(IRI::fromString('http://id.tincanapi.com/extension/color'))->shouldReturn(array(
             'model' => 'RGB',
             'value' => '#FFFFFF',
         ));
 
-        $this->offsetExists(IRI::fromString('http://id.tincanapi.com/extension/starting-position'))->shouldReturn(true);
         $this->offsetGet(IRI::fromString('http://id.tincanapi.com/extension/starting-position'))->shouldReturn(1);
 
         $returnedExtensions = $this->getExtensions();
@@ -54,7 +51,6 @@ function it_throws_exception_when_keys_are_passed_that_are_not_iri_instances_dur
 
     function it_throws_exception_when_keys_are_passed_that_are_not_iri_instances()
     {
-        $this->shouldThrow('\InvalidArgumentException')->during('offsetExists', array('http://id.tincanapi.com/extension/topic'));
         $this->shouldThrow('\InvalidArgumentException')->during('offsetGet', array('http://id.tincanapi.com/extension/topic'));
     }
 
diff --git a/spec/LanguageMapSpec.php b/spec/LanguageMapSpec.php
index 2fa714d..1c884c0 100644
--- a/spec/LanguageMapSpec.php
+++ b/spec/LanguageMapSpec.php
@@ -36,9 +36,7 @@ function it_can_be_created_with_an_existing_array_map()
     function it_returns_a_new_instance_with_an_added_entry()
     {
         $languageTag = $this->withEntry('en-US', 'attended');
-        $languageTag->offsetExists('en-US')->shouldReturn(true);
         $languageTag->shouldNotBe($this);
-        $this->offsetExists('en-US')->shouldReturn(false);
     }
 
     function it_returns_a_new_instance_with_a_modified_entry()
@@ -63,12 +61,6 @@ function it_throws_an_exception_when_a_non_existent_language_tag_is_requested()
         $this->shouldThrow('\InvalidArgumentException')->during('offsetGet', array('en-US'));
     }
 
-    function it_can_be_asked_if_a_language_tag_is_known()
-    {
-        $this->offsetExists('en-GB')->shouldReturn(true);
-        $this->offsetExists('en-US')->shouldReturn(false);
-    }
-
     function its_values_cannot_be_modified()
     {
         $this->shouldThrow('\LogicException')->during('offsetSet', array('en-US', 'attended'));
diff --git a/spec/StateDocumentSpec.php b/spec/StateDocumentSpec.php
index 0fb6657..affc468 100644
--- a/spec/StateDocumentSpec.php
+++ b/spec/StateDocumentSpec.php
@@ -39,11 +39,8 @@ function it_is_a_document()
 
     function its_data_can_be_read()
     {
-        $this->offsetExists('x')->shouldReturn(true);
         $this->offsetGet('x')->shouldReturn('foo');
-        $this->offsetExists('y')->shouldReturn(true);
         $this->offsetGet('y')->shouldReturn('bar');
-        $this->offsetExists('z')->shouldReturn(false);
     }
 
     function it_throws_exception_when_not_existing_data_is_being_read()