Add shadow import failing test.

src/name_analysis/mod.rs

@@ -194,7 +194,29 @@ mod tests {
             ),
         ]);
         let mut symbol_table = SymbolTable::new();
-        add_std_core_symbols(&mut symbol_table).expect("Failed to add std::core symbols.");
         assert_no_diagnostics(sources, &mut symbol_table);
     }
+    
+    #[test]
+    fn shadow_import() {
+        let sources: HashMap<&str, &str> = HashMap::from([
+            (
+                "main.dm",
+                indoc! {"
+                    use greeter::Greeter;
+
+                    class Greeter {}
+                "}
+            ),
+            (
+                "greeter.dm",
+                indoc! {"
+                    ns greeter;
+
+                    class Greeter {}
+                "}
+            )
+        ]);
+        assert_number_of_diagnostics(sources, &mut SymbolTable::new(), 1);
+    }
 }