Contract that must exchange one 3rd party token to its own

Smart Contracts
1

I have a smart contract for exchange USDT to QUE token with rate 1:1

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

contract Question is ERC20 {
    address USDTAddress;
    address BoxAddress;

    constructor(address _USDTAddress) ERC20("Question", "QUE") {
        USDTAddress = _USDTAddress;
        BoxAddress = msg.sender;
    }

    function depositUSDT(uint _tokenAmount) public payable {
        ERC20 USDTToken = ERC20(USDTAddress);
        USDTToken.transferFrom(msg.sender, BoxAddress, _tokenAmount);
        _mint(msg.sender, _tokenAmount);
    }
}

And I wrote a test:

const { expect } = require("chai")
const { ethers, waffle } = require('hardhat')
const { deployContract } = waffle

// contracts
const QJson = require('../artifacts/contracts/Question.sol/Question.json')
const MockUSDT = require('../artifacts/contracts/mocks/mockUSDT.sol/MockUSDT.json')

describe('Question.sol', _ => {
  it('Deposit USDT with Question.sol', async () => {
    const [walletUSDT, walletMatrix] = await ethers.getSigners()

    const tokenUSDT = await deployContract(walletUSDT, MockUSDT)

    // I guess that walletMatrix is a BoxAddress in Question.sol
    // and tokenUSDT.address is a _USDTAddress in a constructor of Question.sol
    const tokenMatrix = await deployContract(walletMatrix, QJson, [
      tokenUSDT.address,
    ])

    // there I put deposit to walletMatrix.address
    await tokenUSDT.connect(walletUSDT).transfer(walletMatrix.address, 11)
    let balance = await tokenUSDT.balanceOf(walletMatrix.address)
    expect(balance).to.equal(11) // ok

    await tokenUSDT.approve(walletMatrix.address, 900)
    // after line below I've got the error:
    await tokenMatrix.connect(walletMatrix).depositUSDT(900)
    // ERC20: transfer amount exceeds balance

    // What's wrong?

    // let matrixBalance = await tokenMatrix.balanceOf(walletMatrix.address)
    // expect(matrixBalance).to.equal(amount2)
  }).timeout(20000)
})

What I do wrong? Maybe I don't understand correctly values in my .sol and .js files?