diff --git a/tests/node-qunit/schema.test.js b/tests/node-qunit/schema.test.js
index 901c1e4ed..757e4cabb 100644
--- a/tests/node-qunit/schema.test.js
+++ b/tests/node-qunit/schema.test.js
@@ -1,13 +1,6 @@
 var mw = mediaWiki,
-	createSchema = require( '../../src/schema' );
-
-function createStubMap() {
-	var m = new Map(); /* global Map */
-	m.get = function ( key, def ) {
-		return Map.prototype.get.call( m, key ) || def;
-	};
-	return m;
-}
+	createSchema = require( '../../src/schema' ),
+	createStubMap = require( './stubs' ).createStubMap;
 
 QUnit.module( 'ext.popups/schema', {
 	setup: function () {
diff --git a/tests/node-qunit/stubs.js b/tests/node-qunit/stubs.js
index 8c10b79c1..048e1ee05 100644
--- a/tests/node-qunit/stubs.js
+++ b/tests/node-qunit/stubs.js
@@ -15,3 +15,22 @@ exports.createStubUser = function createStubUser( isAnon ) {
 		}
 	};
 };
+
+/**
+ * Creates a **minimal** stub that can be used in place of an `mw.Map`
+ * instance.
+ *
+ * @return {mw.Map}
+ */
+exports.createStubMap = function createStubMap() {
+	var m = new Map(); /* global Map */
+	m.get = function ( key, fallback ) {
+		fallback = arguments.length > 1 ? fallback : null;
+		if ( typeof key === 'string' ) {
+			return m.has( key ) ? Map.prototype.get.call( m, key ) : fallback;
+		}
+		// Invalid selection key
+		return null;
+	};
+	return m;
+};