diff --git a/tests/unit/src/Escaper/AbstractEscaperTest.php b/tests/unit/src/Escaper/AbstractEscaperTest.php
index b6529bd..64d0fae 100644
--- a/tests/unit/src/Escaper/AbstractEscaperTest.php
+++ b/tests/unit/src/Escaper/AbstractEscaperTest.php
@@ -1,6 +1,14 @@
 <?php
 namespace Aura\Html\Escaper;
 
+use Aura\Html\FakePhp;
+
+// trick PHP into using this function instead of the native function
+function function_exists($name)
+{
+    return FakePhp::function_exists($name);
+}
+
 /**
  *
  * Based almost entirely on Zend\Escaper by Padraic Brady et al. and modified
@@ -15,6 +23,21 @@ abstract class AbstractEscaperTest extends \PHPUnit_Framework_TestCase
 
     abstract public function test__construct();
 
+    protected function setUp()
+    {
+        FakePhp::$function_exists['iconv'] = \function_exists('iconv');
+        FakePhp::$function_exists['mb_convert_encoding'] = \function_exists('mb_convert_encoding');
+    }
+
+    public function testMissingExtensions()
+    {
+        FakePhp::$function_exists['iconv'] = false;
+        FakePhp::$function_exists['mb_convert_encoding'] = false;
+        $this->escaper->setEncoding('iso8859-1');
+        $this->setExpectedException('Aura\Html\Exception\ExtensionNotInstalled');
+        $this->escaper->toUtf8('x');
+    }
+
     public function testSetAndGetEncoding()
     {
         $this->escaper->setEncoding('macroman');
diff --git a/tests/unit/src/Escaper/AttrEscaperTest.php b/tests/unit/src/Escaper/AttrEscaperTest.php
index 40372ad..bedec02 100644
--- a/tests/unit/src/Escaper/AttrEscaperTest.php
+++ b/tests/unit/src/Escaper/AttrEscaperTest.php
@@ -13,6 +13,7 @@ class AttrEscaperTest extends AbstractEscaperTest
 {
     public function setUp()
     {
+        parent::setUp();
         $this->escaper = new AttrEscaper(new HtmlEscaper);
     }
 
diff --git a/tests/unit/src/Escaper/CssEscaperTest.php b/tests/unit/src/Escaper/CssEscaperTest.php
index 14b2472..88067ca 100644
--- a/tests/unit/src/Escaper/CssEscaperTest.php
+++ b/tests/unit/src/Escaper/CssEscaperTest.php
@@ -13,6 +13,7 @@ class CssEscaperTest extends AbstractEscaperTest
 {
     public function setUp()
     {
+        parent::setUp();
         $this->escaper = new CssEscaper;
     }
 
diff --git a/tests/unit/src/Escaper/HtmlEscaperTest.php b/tests/unit/src/Escaper/HtmlEscaperTest.php
index b139a0a..1b90bc1 100644
--- a/tests/unit/src/Escaper/HtmlEscaperTest.php
+++ b/tests/unit/src/Escaper/HtmlEscaperTest.php
@@ -13,6 +13,7 @@ class HtmlEscaperTest extends AbstractEscaperTest
 {
     public function setUp()
     {
+        parent::setUp();
         $this->escaper = new HtmlEscaper;
     }
 
diff --git a/tests/unit/src/Escaper/JsEscaperTest.php b/tests/unit/src/Escaper/JsEscaperTest.php
index 4f65a53..b6240c2 100644
--- a/tests/unit/src/Escaper/JsEscaperTest.php
+++ b/tests/unit/src/Escaper/JsEscaperTest.php
@@ -13,6 +13,7 @@ class JsEscaperTest extends AbstractEscaperTest
 {
     public function setUp()
     {
+        parent::setUp();
         $this->escaper = new JsEscaper;
     }
 
diff --git a/tests/unit/src/FakePhp.php b/tests/unit/src/FakePhp.php
new file mode 100644
index 0000000..8377b42
--- /dev/null
+++ b/tests/unit/src/FakePhp.php
@@ -0,0 +1,12 @@
+<?php
+namespace Aura\Html;
+
+class FakePhp
+{
+    static public $function_exists = array();
+
+    static public function function_exists($name)
+    {
+        return self::$function_exists[$name];
+    }
+}