Add qualified opaque reference reporting test

reporting/tests/test_reporting.rs

@@ -8199,4 +8199,39 @@ I need all branches in an `if` to have the same type!
             ),
         )
     }
+
+    #[test]
+    fn qualified_opaque_reference() {
+        report_problem_as(
+            indoc!(
+                r#"
+                OtherModule.$Age 21
+                "#
+            ),
+            // TODO: get rid of the second error. Consider parsing OtherModule.$Age to completion
+            // and checking it during can.
+            indoc!(
+                r#"
+                ── SYNTAX PROBLEM ──────────────────────────────────────────────────────────────
+
+                I am trying to parse a qualified name here:
+
+                1│  OtherModule.$Age 21
+                                ^
+
+                I was expecting to see an identifier next, like height. A complete
+                qualified name looks something like Json.Decode.string.
+
+                ── OPAQUE NOT DEFINED ──────────────────────────────────────────────────────────
+
+                The opaque type Age referenced here is not defined:
+
+                1│  OtherModule.$Age 21
+                                ^^^^
+
+                Note: It looks like there are no opaque types declared in this module yet!
+                "#
+            ),
+        )
+    }
 }