diff -r 000000000000 -r 6474c204b198 dom/bindings/parser/tests/test_promise.py
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dom/bindings/parser/tests/test_promise.py	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,63 @@
+def WebIDLTest(parser, harness):
+    threw = False
+    try:
+        parser.parse("""
+            interface Promise {};
+            interface A {
+              legacycaller Promise foo();
+            };
+        """)
+        results = parser.finish()
+
+    except:
+        threw = True
+    harness.ok(threw,
+               "Should not allow Promise return values for legacycaller.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse("""
+            interface Promise {};
+            interface A {
+              Promise foo();
+              long foo(long arg);
+            };
+        """)
+        results = parser.finish();
+    except:
+        threw = True
+    harness.ok(threw,
+               "Should not allow overloads which have both Promise and "
+               "non-Promise return types.")
+
+    parser = parser.reset()
+    threw = False
+    try:
+        parser.parse("""
+            interface Promise {};
+            interface A {
+              long foo(long arg);
+              Promise foo();
+            };
+        """)
+        results = parser.finish();
+    except:
+        threw = True
+    harness.ok(threw,
+               "Should not allow overloads which have both Promise and "
+               "non-Promise return types.")
+
+    parser = parser.reset()
+    parser.parse("""
+        interface Promise {};
+        interface A {
+          Promise foo();
+          Promise foo(long arg);
+        };
+    """)
+    results = parser.finish();
+
+    harness.ok(True,
+               "Should allow overloads which only have Promise and return "
+               "types.")