changed price converter to use aggregator v3 and changed mock tests

contracts/dependencies/PriceConverter.sol

@@ -3,16 +3,42 @@ pragma solidity 0.8.9;
 
 import '@openzeppelin/contracts/access/Ownable.sol';
 
-interface AggregatorInterface {
-	function latestAnswer() external view returns (int256);
+interface AggregatorV3Interface {
+	function decimals() external view returns (uint8);
+
+	function description() external view returns (string memory);
+
+	function version() external view returns (uint256);
+
+	function getRoundData(uint80 _roundId)
+		external
+		view
+		returns (
+			uint80 roundId,
+			int256 answer,
+			uint256 startedAt,
+			uint256 updatedAt,
+			uint80 answeredInRound
+		);
+
+	function latestRoundData()
+		external
+		view
+		returns (
+			uint80 roundId,
+			int256 answer,
+			uint256 startedAt,
+			uint256 updatedAt,
+			uint80 answeredInRound
+		);
 }
 
 contract PriceConverter is Ownable {
 	/// Oracle feed pricing
-	AggregatorInterface public priceFeedContract;
+	AggregatorV3Interface public priceFeedContract;
 
 	constructor(address _priceAggregator) {
-		priceFeedContract = AggregatorInterface(_priceAggregator);
+		priceFeedContract = AggregatorV3Interface(_priceAggregator);
 	}
 
 	/**
@@ -37,15 +63,24 @@ contract PriceConverter is Ownable {
 	 * @dev Returns the latest price
 	 */
 	function getEtherPriceInUSD() public view returns (uint256) {
-		int256 answer = priceFeedContract.latestAnswer();
-		// Chainlink returns 8 decimal places so we convert to wei
-		return uint256(answer * 1e10);
+		(uint80 roundID, int256 answer, , uint256 updatedAt, uint80 answeredInRound) = priceFeedContract.latestRoundData();
+
+		// check that answer is indeed from the last known round
+		require(answeredInRound == roundID, 'Stale price');
+		// check that answer is within an allowed margin of freshness by checking updated at was updated less than an hour ago
+		require(updatedAt > block.timestamp - 3600, 'Answer is not from last known round');
+		// check returned answer is not zero
+		require(answer > 0, 'Negative price');
+
+		// safe to cast answer into uint256 as we require it to be greater than 0 or above and decimals returns a uint8
+		// this also assumes that aggregator decimals won't surpass 18 as it will revert with a panic error also solidity doesn't support negative exponents yet
+		return uint256(answer) * (10**(18 - priceFeedContract.decimals()));
 	}
 
 	/**
 	 * @dev changes the price aggregator
 	 */
-	function changeAggregator(AggregatorInterface _priceFeedContract) external onlyOwner {
+	function changeAggregator(AggregatorV3Interface _priceFeedContract) external onlyOwner {
 		priceFeedContract = _priceFeedContract;
 	}
 }

contracts/mocks/DummyPriceOracle.sol

@@ -1,12 +1,41 @@
 // SPDX-License-Identifier: MIT
 pragma solidity >=0.8.9;
 
-interface AggregatorInterface {
-	function latestAnswer() external view returns (int256);
+interface AggregatorV3Interface {
+	function decimals() external view returns (uint8);
+
+	function description() external view returns (string memory);
+
+	function version() external view returns (uint256);
+
+	function getRoundData(uint80 _roundId)
+		external
+		view
+		returns (
+			uint80 roundId,
+			int256 answer,
+			uint256 startedAt,
+			uint256 updatedAt,
+			uint80 answeredInRound
+		);
+
+	function latestRoundData()
+		external
+		view
+		returns (
+			uint80 roundId,
+			int256 answer,
+			uint256 startedAt,
+			uint256 updatedAt,
+			uint80 answeredInRound
+		);
 }
 
-contract DummyPriceOracle is AggregatorInterface {
+contract DummyPriceOracle is AggregatorV3Interface {
 	int256 value;
+	uint8 _decimals = 8;
+	string _description = '';
+	uint256 _version = 3;
 
 	constructor(int256 _value) {
 		set(_value);
@@ -16,7 +45,49 @@ contract DummyPriceOracle is AggregatorInterface {
 		value = _value;
 	}
 
-	function latestAnswer() external view returns (int256) {
-		return value;
+	function setDecimals(uint8 __decimals) external {
+		_decimals = __decimals;
+	}
+
+	function decimals() external view returns (uint8) {
+		return _decimals;
+	}
+
+	function description() external view returns (string memory) {
+		return _description;
+	}
+
+	function version() external view returns (uint256) {
+		return _version;
+	}
+
+	function getRoundData(
+		uint80 /** _roundId */
+	)
+		external
+		view
+		returns (
+			uint80 roundId,
+			int256 answer,
+			uint256 startedAt,
+			uint256 updatedAt,
+			uint80 answeredInRound
+		)
+	{
+		return (1, value, block.timestamp, block.timestamp, 1);
+	}
+
+	function latestRoundData()
+		external
+		view
+		returns (
+			uint80 roundId,
+			int256 answer,
+			uint256 startedAt,
+			uint256 updatedAt,
+			uint80 answeredInRound
+		)
+	{
+		return (1, value, block.timestamp, block.timestamp, 1);
 	}
 }