function _deposit(uint256 assets, address receiver)
    internal
    returns (uint256 shares)
{
    uint256 _pool = underlyingBalance();
    uint256 _before = underlyingToken.balanceOf(address(this));

    // **Assume caller is depositor**
    underlyingToken.transferFrom(msg.sender, address(this), assets);
    uint256 _after = underlyingToken.balanceOf(address(this));
    assets = _after.sub(_before); // Additional check for deflationary tokens
    ...
-   preBalance  = `100_000e18`;
-   `underlyingToken.transferFrom(msg.sender, address(this), 1)`
