chore: test refactoring - checking for nullability by using XCTAssertNotNil

Author: JeneaVranceanu

Tests/web3swiftTests/localTests/ERC20Tests.swift

@@ -26,10 +26,10 @@ class ERC20Tests: LocalTestCase {
 
         let addressOfUser = EthereumAddress("0xe22b8979739D724343bd002F9f432F5990879901")!
         let contract = web3.contract(Web3.Utils.erc20ABI, at: receipt.contractAddress!, abiVersion: 2)!
-        guard let readTX = contract.createReadOperation("balanceOf", parameters: [addressOfUser]) else {return XCTFail()}
+        guard let readTX = contract.createReadOperation("balanceOf", parameters: [addressOfUser]) else { return XCTFail() }
         readTX.transaction.from = addressOfUser
-        let tokenBalance = try await readTX.callContractMethod()
-        guard let bal = tokenBalance["0"] as? BigUInt else {return XCTFail()}
+        let tokenBalanceResponse = try await readTX.callContractMethod()
+        XCTAssertNotNil(tokenBalanceResponse["0"] as? BigUInt)
     }
 
     // FIXME: Make me work