It's important to consider two scenarios: either client.guilds is undefined or guild.members is undefined.
If client is properly defined and testserver has a valid guild ID, then both client.guilds and guild.members will be defined. However, if client is undefined, you may encounter an error similar to the one you're experiencing. Ensure that your client variable is defined with value; if not, use message.client instead.
Additionally, verify that your testserver variable is defined with a valid ID. This is likely causing the issue. Have you created a testserver variable in this file? Is it correctly set up with a valid ID?
To handle such issues more effectively, separate getting your guild, member, and user:
const guild = message.client.guilds.resolve(testserver);
if (!guild) return message.channel.send("Couldn't find the guild!")
let myMember = guild.members.resolve(creator);
if (!myMember) return message.channel.send("Couldn't find the user!")
const myUser = myMember.user;
This approach not only follows best practices but also handles cases where the guild or user can't be found. It's crucial because if you fail to locate and store the user in a variable, it could impact other parts of your code that rely on it. Moreover, it helps pinpoint any issues within your code by indicating whether the correct guild/user couldn't be found.