add mint flow tests and extend ZToken mock for internal logic

Author: ademolahh

src/ZToken.sol

@@ -39,8 +39,20 @@ abstract contract ZToken is IZToken, ERC20 {
         borrowIndex = 1e18;
     }
 
+    function _mint(uint256 _zTokenAmount) internal returns (uint256) { }
+
     function _getUtilization() internal pure returns (uint256) { }
 
+    function getTotalCash() external view returns (uint256) {
+        return totalCash;
+    }
+
+    function getReserves() external view returns (uint256) {
+        return totalReserve;
+    }
+
+    function getExchangeRate() external view returns (uint256) { }
+
     function getUnderlyingToken() external view returns (address) {
         return UNDERLYING_TOKEN;
     }

test/mocks/ZTokenMock.sol

@@ -5,6 +5,12 @@ import { IZToken, ZToken } from "src/ZToken.sol";
 
 contract ZTokenMock is ZToken {
     constructor(IZToken.MarketConfig memory _config) ZToken(_config) { }
+
+    function mint(uint256 _zTokenAmount) external returns (uint256) {
+        uint256 underLyingAmount = _mint(_zTokenAmount);
+        return underLyingAmount;
+    }
+
     function name() public view override returns (string memory) { }
     function symbol() public view override returns (string memory) { }
 }

test/unit/ZToken.t.sol

@@ -1,11 +1,16 @@
 // SPDX-License-Identifier: UNLICENSED
 pragma solidity 0.8.28;
 
-import { Test } from "forge-std/Test.sol";
-import { IZToken, ZTokenMock } from "../mocks/ZTokenMock.sol";
-import { MockERC20 } from "../mocks/MockERC20.sol";
+import {Test} from "forge-std/Test.sol";
+
+import {IZToken, ZTokenMock} from "../mocks/ZTokenMock.sol";
+import {MockERC20} from "../mocks/MockERC20.sol";
+import {FixedPointMathLib} from "solady/utils/FixedPointMathLib.sol";
+import {IERC20} from "forge-std/interfaces/IERC20.sol";
 
 contract ZToken is Test {
+    using FixedPointMathLib for uint256;
+
     ZTokenMock public zToken;
     MockERC20 public underlyingToken;
 
@@ -43,15 +48,33 @@ contract ZToken is Test {
 
     function test_Mint_WhenTheAmountIsZero() external {
         // it reverts
-        vm.skip(true);
+        vm.expectRevert();
+        zToken.mint(0);
     }
 
-    function test_Mint_WhenTheAmountIsGreaterThanZero() external {
+    function test_Mint_WhenTheAmountIsGreaterThanZero(uint256 _zTokenAmount) external {
+        _minValue(_zTokenAmount);
+
+        uint256 underlyingTokenAmount = zToken.mint(_zTokenAmount);
+
         // it converts the zToken amount to underlying value
+        assertEq(zToken.getExchangeRate().mulDiv(_zTokenAmount, FixedPointMathLib.WAD), underlyingTokenAmount);
         // it transfers the underlying tokens to the contract
+        assertEq(IERC20(address(underlyingToken)).balanceOf(address(zToken)), underlyingTokenAmount);
         // it mints the corresponding zTokens to the user
+        assertEq(zToken.balanceOf(address(this)), _zTokenAmount);
         // it updates the total cash balance
+        assertEq(zToken.getTotalCash(), underlyingTokenAmount);
         // it updates the reserve values and interest rate
-        vm.skip(true);
+        assertEq(zToken.getReserves(), 0);
+    }
+
+    function test_Mint_WhenMultipleDepositAtInterval() external {
+        // it reserve should be zero
+        // it interest rate should still be zerp
+    }
+
+    function _minValue(uint256 _amount) internal view {
+        _amount = bound(_amount, 1e18, type(uint64).max);
     }
 }

test/unit/ZToken.tree

@@ -12,9 +12,13 @@ ZToken::constructor
 ZToken::mint
 ├── when the amount is zero
 │   └── it reverts
-└── when the amount is greater than zero
-    ├── it converts the zToken amount to underlying value
-    ├── it transfers the underlying tokens to the contract
-    ├── it mints the corresponding zTokens to the user
-    ├── it updates the total cash balance
-    └── it updates the reserve values and interest rate
+├── when the amount is greater than zero
+│   ├── it converts the zToken amount to underlying value
+│   ├── it transfers the underlying tokens to the contract
+│   ├── it mints the corresponding zTokens to the user
+│   ├── it updates the total cash balance
+│   ├── it updates the reserve values and interest rate
+│   └── it borrow snapshot should be initial borrow index
+└── when multiple deposit at interval
+    ├── it reserve should be zero
+    └── it interest rate should still be zerp