test.cs

public static bool WriteValue(string username, FormField[] formFields) {

  List<Deployment> deployments = GetDeployments();

  foreach (Deployment deployment in deployments) {
    if (deployment.Username == username) {
      deployment.FormFields = formFields;

      System.IO.File.WriteAllText("App_Data/deployments.json", 
                                  JsonConvert.SerializeObject(deployments));

      return true;
    }
  }

  return false;
}