Hi, thanks you for the Course, but i mention the it's possible to send minus or 0 value on amount and i think it's will be very danger.
specially for people will really run it as a production.

you can send minus amount on create Transaction eg

it will rise sender balance :) for sure -- = +
fix need 2 tests + 2 fix on classes
wallet / index.test.js

			it("throws an error on mins", () => {
				expect(() => {
					wallet.createTransaction({
						recipient: "arabto2-recipient",
						amount: -100,
					});
				}).toThrow("incorrect amount value");
			});

wallet/ index.js

		if (amount <= 0) {
			throw new Error("incorrect amount value");
		} 

------ also on update transaction -----
wallet/transaction.test.js

			it("throws an error on mins", () => {
				expect(() => {
					transaction.update({
						senderWallet,
						recipient: "arabto2-recipient",
						amount: -100,
					});
				}).toThrow("incorrect amount value");
			});

wallet/transaction.js

		if (amount <= 0) {
			throw new Error("incorrect amount value");
		}

also i think it balance shall not accept minus value , the amount also accept alphabet so i even suggest to have method on util to validate the number