spec: resolve on process exited

src/spec.ts

@@ -458,6 +458,9 @@ export async function watchSPEC<T extends ChildProcessByStdio<null | Writable, R
             }
         });
         process.on("error", error => reject(error));
+        process.on("close", () => resolve({
+            outputFiles
+        }));
     });
 }