diff --git a/test/test-interface-extend.js b/test/test-interface-extend.js
new file mode 100644
index 0000000..2b2310e
--- /dev/null
+++ b/test/test-interface-extend.js
@@ -0,0 +1,61 @@
+/**
+ * Tests extending of interfaces
+ *
+ *  Copyright (C) 2010 Mike Gerwitz
+ *
+ *  This file is part of ease.js.
+ *
+ *  ease.js is free software: you can redistribute it and/or modify it under the
+ *  terms of the GNU Lesser 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 Lesser General Public License
+ *  for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * @author  Mike Gerwitz
+ * @package test
+ */
+
+require( './common' );
+
+var assert         = require( 'assert' ),
+    Interface      = require( 'interface' ),
+    abstractMethod = Interface.abstractMethod;
+
+
+assert.throws( function()
+{
+    Interface.extend(
+    {
+        // properties (non-methods) are not permitted
+        prop: 'not permitted',
+    });
+}, Error, "Properties are not permitted within Interface definitions" );
+
+assert.throws( function()
+{
+    Interface.extend(
+    {
+        // concrete method
+        method: function() {}
+    });
+}, Error, "Concrete methods are not permitted within Interface definitions" );
+
+assert.doesNotThrow(
+    function()
+    {
+        Interface.extend(
+        {
+            method: abstractMethod(),
+        });
+    },
+    Error,
+    "Abstract method declarations are allowed within Interface definitions"
+);
+
diff --git a/test/test-interface.js b/test/test-interface.js
index 073229f..05b6cb2 100644
--- a/test/test-interface.js
+++ b/test/test-interface.js
@@ -42,34 +42,3 @@ assert.equal(
     "Generated interface object should be frozen"
 );
 
-
-assert.throws( function()
-{
-    Interface.extend(
-    {
-        // properties (non-methods) are not permitted
-        prop: 'not permitted',
-    });
-}, Error, "Properties are not permitted within Interface definitions" );
-
-assert.throws( function()
-{
-    Interface.extend(
-    {
-        // concrete method
-        method: function() {}
-    });
-}, Error, "Concrete methods are not permitted within Interface definitions" );
-
-assert.doesNotThrow(
-    function()
-    {
-        Interface.extend(
-        {
-            method: abstractMethod(),
-        });
-    },
-    Error,
-    "Abstract method declarations are allowed within Interface definitions"
-);
-