Add a closure test.

test/closure/reuse_closure_slot.wren

@@ -15,4 +15,3 @@
 }
 
 // TODO: Maximum number of closed-over variables (directly and/or indirect).
-// TODO: Shadow variable used in closure.

test/closure/shadow_closure_with_local.wren

@@ -0,0 +1,11 @@
+{
+  var foo = "closure"
+  new Fn {
+    {
+      IO.print(foo) // expect: closure
+      var foo = "shadow"
+      IO.print(foo) // expect: shadow
+    }
+    IO.print(foo) // expect: closure
+  }.call
+}