Testing, Debugging, and Auditing Contracts BDC Practice Questions (Page 6)

Questions 26–30

1. 26application · medium

   A developer wants to automatically detect common vulnerabilities like integer overflow and unprotected selfdestruct in a Solidity contract before deploying. Which tool should the developer use?

   • AOpenZeppelin's test helpers, which provide assertions for unit tests.
   • BSlither, a static analysis framework that runs a set of detectors for known vulnerabilities.
   • CGanache, a personal blockchain for testing transactions.
   • DRemix IDE's debugger, which steps through transactions.
   Reveal Solution Discussion Select an answer first
2. 27application · medium

   A developer is debugging a contract that is consuming an unexpectedly high amount of gas. The contract has a loop that iterates over an array. Which debugging technique is most effective to identify the gas issue?

   • ARemove the loop and hardcode the array elements to reduce gas.
   • BRun a static analysis tool to detect gas-heavy patterns.
   • CUse a gas profiler or the test framework's gas reporting to see which operations consume the most gas.
   • DAdd `console.log` statements inside the loop to print the loop index.
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4. 28expert · hard

   A developer is using a formal verification tool to prove that a contract's `transfer` function never allows a user's balance to become negative. The tool requires the developer to specify preconditions and postconditions. Which of the following is a necessary precondition for this property?

   • AThe function is marked `external` to prevent internal calls.
   • BThe recipient's balance is less than the maximum uint256 value.
   • CThe caller's balance is greater than or equal to the transfer amount.
   • DThe contract has a reentrancy guard.
   Reveal Solution Discussion Select an answer first
5. 29foundation · easy

   Why is testing considered essential in smart contract development?

   • ABecause testing is the only way to deploy a contract to the mainnet.
   • BBecause testing is required by law for all blockchain applications.
   • CBecause smart contracts are immutable after deployment, so bugs cannot be patched easily.
   • DBecause testing guarantees that the contract will never have any security issues.
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6. 30application · medium

   A smart contract has a function that updates a user's balance after sending Ether to the user. An auditor suspects a reentrancy vulnerability. Which code pattern is most likely vulnerable?

   • AThe function uses a `require` statement to check the user's balance before sending Ether.
   • BThe function sends Ether to the user first, then updates the user's balance.
   • CThe function updates the user's balance first, then sends Ether to the user.
   • DThe function uses `transfer` instead of `call` to send Ether.
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