diff -r 000000000000 -r 6474c204b198 dom/bindings/parser/tests/test_mozmap.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dom/bindings/parser/tests/test_mozmap.py	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,39 @@
+import WebIDL
+
+def WebIDLTest(parser, harness):
+    parser.parse("""
+        dictionary Dict {};
+        interface MozMapArg {
+          void foo(MozMap<Dict> arg);
+        };
+    """)
+
+    results = parser.finish()
+
+    harness.check(len(results), 2, "Should know about two things");
+    harness.ok(isinstance(results[1], WebIDL.IDLInterface),
+               "Should have an interface here");
+    members = results[1].members
+    harness.check(len(members), 1, "Should have one member")
+    harness.ok(members[0].isMethod(), "Should have method")
+    signature = members[0].signatures()[0]
+    args = signature[1]
+    harness.check(len(args), 1, "Should have one arg")
+    harness.ok(args[0].type.isMozMap(), "Should have a MozMap type here")
+    harness.ok(args[0].type.inner.isDictionary(),
+               "Should have a dictionary inner type")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse("""
+            interface MozMapVoidArg {
+              void foo(MozMap<void> arg);
+            };
+        """)
+
+        results = parser.finish()
+    except Exception,x:
+        threw = True
+
+    harness.ok(threw, "Should have thrown.")