Test case for #3950 (#3958)

vsintegration/tests/unittests/UnusedOpensTests.fs

@@ -371,6 +371,21 @@ let _ = func()
 """
     => []
 
+[<Test>]
+let ``auto open module with namespace``() =
+    """
+namespace Module1Namespace
+[<AutoOpen>]
+module Module1 =
+    module Module2 =
+        let x = 1
+namespace ConsumerNamespace
+open Module1Namespace
+module Module3 =
+            let y = Module2.x
+"""
+    => []
+
 [<Test>]
 let ``auto open module in the middle of hierarchy``() =
     """
@@ -736,4 +751,4 @@ module M2 =
     open M1
     let _ = T()
 """
-    => []
\ No newline at end of file
+    => []