add MockERC20 with permit

Author: alexcos20

contracts/utils/mock/MockERC20Permit.sol

@@ -0,0 +1,37 @@
+pragma solidity 0.8.12;
+// Copyright BigchainDB GmbH and Ocean Protocol contributors
+// SPDX-License-Identifier: (Apache-2.0 AND CC-BY-4.0)
+// Code is Apache-2.0 and docs are CC-BY-4.0
+
+import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
+import "@openzeppelin/contracts/token/ERC20/extensions/ERC20Permit.sol";
+
+/**
+ * @dev Mock ERC20 token with configurable decimals and ERC20Permit support.
+ *      This is a test utility contract that implements ERC20Permit for testing permit functionality.
+ */
+contract MockERC20Permit is ERC20, ERC20Permit {
+    uint8 private _decimals;
+
+    /**
+     * @dev Sets the values for {name}, {symbol}, and {decimals}.
+     * @param name_ Token name
+     * @param symbol_ Token symbol
+     * @param decimals_ Number of decimals
+     */
+    constructor(
+        string memory name_,
+        string memory symbol_,
+        uint8 decimals_
+    ) ERC20(name_, symbol_) ERC20Permit(name_) {
+        _decimals = decimals_;
+        _mint(msg.sender, 10e25);
+    }
+
+    /**
+     * @dev Returns the number of decimals used to get its user representation.
+     */
+    function decimals() public view virtual override returns (uint8) {
+        return _decimals;
+    }
+}