added cbEthRateProvider and tests

contracts/CBETHRateProvider.sol

@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.4;
+
+import "./interfaces/IcbETH.sol";
+import "./interfaces/IRateProvider.sol";
+
+
+/**
+ * @title Coinbase wrapped staked Eth Rate Provider
+ * @notice Returns value of cbEth in terms of Eth
+ */
+contract CbEthRateProvider is IRateProvider {
+    IcbETH public immutable cbETH;
+    address public origin;
+
+    constructor(IcbETH _cbETH) {
+        cbETH = _cbETH;
+
+    }
+
+    /**
+     * @return value of cbETH in terms of Eth scaled by 10**18
+     */
+    function getRate() public view override returns (uint256) {
+        return cbETH.exchangeRate();
+    }
+}

contracts/interfaces/IcbETH.sol

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+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.4;
+
+
+
+/**
+ * @title Coinbase Staked ETH interface to return exchangeRate
+ * @dev 
+ *
+ */
+interface IcbETH {
+    /**
+     * @notice get exchange rate
+     * @return Returns the current exchange rate scaled by by 10**18
+     */
+    function exchangeRate() external view returns (uint256);
+}

contracts/test/MockCBEth.sol

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+//SPDX-License-Identifier: MIT
+
+pragma solidity^0.8.4;
+
+contract MockCBEth {
+    uint256 private _exchangeRate = 1; 
+
+    function exchangeRate() external view returns(uint256){
+        return _exchangeRate*1e18;
+    } 
+
+    // anyone can set the rate in this mock example
+    function setExchangeRate(uint256 newRate) external {
+        _exchangeRate = newRate;
+    }
+}
+
+

test/cbEthRateProvider.test.ts

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+import { ethers } from 'hardhat';
+import { expect } from 'chai';
+import { Contract } from 'ethers';
+import { SignerWithAddress } from '@nomiclabs/hardhat-ethers/dist/src/signer-with-address';
+
+
+describe('Coinbase Eth rate provider', function() {
+    let mockCBEth: Contract;
+    let cBEthRateProvider: Contract;
+    let signer: SignerWithAddress;
+    let tempAddress;
+
+    before('setup eoas', async () => {
+        [signer, ] = await ethers.getSigners();
+    })
+
+    beforeEach('deploy mock & rate provider', async () =>{
+        const MockCBEth = await ethers.getContractFactory('MockCBEth');
+        mockCBEth = await MockCBEth.deploy();
+        tempAddress = mockCBEth.address;
+        const CBEthRateProvider = await ethers.getContractFactory('CbEthRateProvider');
+        cBEthRateProvider = await CBEthRateProvider.deploy(tempAddress);
+
+    })
+
+    it('returns rate scaled correctly', async () => {
+        expect(await mockCBEth.exchangeRate()).to.equal(ethers.utils.parseUnits('1', 18));
+    })
+    it('can set rate', async () => {
+        await mockCBEth.setExchangeRate(2)
+        expect(await mockCBEth.exchangeRate()).to.equal(ethers.utils.parseUnits('2', 18));
+    })
+    it('gets rate from rateProvider',async () => {
+        expect(await cBEthRateProvider.getRate()).to.equal(ethers.utils.parseUnits('1', 18));
+    })
+    it('gets correct rate from rateProvider after underlying rate update',async () => {
+        await mockCBEth.setExchangeRate(2);
+        expect(await cBEthRateProvider.getRate()).to.equal(ethers.utils.parseUnits('2', 18));
+    })
+})

test/chEthRateProviderMainnetFork.test.ts

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+import { ethers } from 'hardhat';
+import { expect, assert } from 'chai';
+import { BigNumber, Contract } from 'ethers';
+import { SignerWithAddress } from '@nomiclabs/hardhat-ethers/dist/src/signer-with-address';
+
+
+
+describe('Coinbase Eth rate provider', function() {
+    let cBEthRateProvider: Contract;
+    let signer: SignerWithAddress;
+    let cbEthAddres = '0xBe9895146f7AF43049ca1c1AE358B0541Ea49704'; //mainnet
+
+    before('setup eoas', async () => {
+        [signer, ] = await ethers.getSigners();
+    })
+
+    beforeEach('deploy rate provider', async () =>{
+        const CBEthRateProvider = await ethers.getContractFactory('CbEthRateProvider');
+        cBEthRateProvider = await CBEthRateProvider.deploy(cbEthAddres);
+    })
+    it('checks if proxy = asset in rate provider',async () => {
+        expect(await cBEthRateProvider.cbETH()).to.equal(cbEthAddres)
+    })
+    it('greater than 18 decimals scale - scaled',async () => {
+        let currentRate = await cBEthRateProvider.getRate();
+        expect(currentRate.gt(BigNumber.from(10).pow(18))).to.be.true;
+    })
+    it('is lower than 19 decimals - scaled',async () => {
+        let currentRate = await cBEthRateProvider.getRate();
+        expect(currentRate.lt(BigNumber.from(10).pow(19))).to.be.true;
+    })
+})