Additional tests for BWU (#74)

engine/src/module/wit_instance.rs

@@ -131,10 +131,7 @@ impl WITInstance {
 
                     Ok((start_index + idx as usize, func))
                 }
-                None => Err(FCEError::NoSuchModule(format!(
-                    "trying to get imports from module with name {} that is not loaded",
-                    import.namespace
-                ))),
+                None => Err(FCEError::NoSuchModule(import.namespace.to_string())),
             })
             .collect::<FCEResult<HashMap<_, _>>>()
     }