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https://github.com/zororaka00/solidity-engineer-interview-test-code

Tutorial Solidity Engineer Interview Test Code
https://github.com/zororaka00/solidity-engineer-interview-test-code

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Tutorial Solidity Engineer Interview Test Code

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# Solidity Engineer Interview Tutorial



Welcome to the interview tutorial for the **Solidity Engineer** position. This interview is divided into three sessions based on the candidate's experience level: **Junior**, **Middle**, and **Senior**. Each session contains both theory questions and practical coding tasks to be completed or optionally attempted by the candidate.



## Reason for Creating This Repository



I created this repository because I noticed that many HR professionals are often confused about the technical requirements and standards needed for the Solidity Engineer position. Therefore, I wanted to create a comprehensive and accessible resource to help both HR professionals and candidates understand what is expected during an interview.



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## Interview Sessions



### 1. **Junior Solidity Engineer**



**Goal:** To test the candidate’s basic understanding of Solidity, smart contract structure, and ability to complete simple tasks.



#### Theory Questions:

- What is a smart contract in the context of blockchain? Explain how it works and its functions.

- What are the differences between `public`, `internal`, and `private` modifiers in Solidity?

- Explain what Gas is and how Gas works during transaction execution in Ethereum.

- What are `require()` and `assert()` in Solidity? Explain the differences and their usage.



#### Practical Tasks (Mandatory):

1. Create a simple smart contract that allows users to store and retrieve an integer (`uint256`).

   - Functions: `storeNumber(uint256 _number)` to store a number, and `getNumber()` to retrieve the stored number.

   - **Unit Testing:** Write unit tests to verify that numbers can be stored and retrieved correctly.

   - **Documentation:** Provide comments in your code explaining each function's purpose.



2. Implement a function that allows users to reset the stored number to zero.

   - Function: `resetNumber()`.

   - **Unit Testing:** Write tests to ensure that the reset functionality works as expected.

   - **Documentation:** Include explanations of how this function interacts with other functions.



3. Add an event that logs when a number is stored.

   - Event: `NumberStored(uint256 indexed _number)`.

   - **Unit Testing:** Test that the event is emitted correctly when a number is stored.

   - **Documentation:** Explain the significance of events in smart contracts.



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### 2. **Middle Solidity Engineer**



**Goal:** To assess the candidate’s deeper understanding of smart contracts, gas optimization, access control, and library usage.



#### Theory Questions:

- Explain the concept of **Inheritance** in Solidity and provide an example of its usage.

- What is a **Reentrancy Attack** and how can it be prevented in smart contracts?

- How is **Gas optimization** achieved in Solidity contracts? Provide tips and tricks to reduce gas consumption.

- What is a **fallback function** and how is it used in a smart contract?



#### Practical Tasks (Mandatory):

1. Create a smart contract that stores balances in the form of **ERC20 tokens** using OpenZeppelin's ERC20 implementation. Allow users to transfer tokens and track their balances.

   - Functions: `transfer(address _to, uint256 _amount)` and `balanceOf(address _account)`.

   - **Unit Testing:** Write tests to verify correct token transfers and balance tracking.

   - **Documentation:** Document each function's purpose and how it interacts with OpenZeppelin's ERC20 library.



2. Implement a function that allows users to approve another address to spend tokens on their behalf using OpenZeppelin’s `approve` method.

   - Function: `approve(address _spender, uint256 _amount)`.

   - **Unit Testing:** Ensure that approval works correctly by testing various scenarios.

   - **Documentation:** Explain how approvals work within ERC20 standards.



3. Create a simple voting mechanism that allows token holders to vote on proposals where each vote is weighted by the amount of tokens held.

   - Features: `vote(uint256 proposalId)` where each vote counts based on token balance.

   - **Unit Testing:** Write tests to validate that votes are counted correctly based on token holdings.

   - **Documentation:** Provide an overview of how voting rights are determined by token ownership.



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### 3. **Senior Solidity Engineer**



**Goal:** To evaluate the candidate’s ability to design complex smart contract systems, manage high-level security, and implement efficient patterns.



#### Theory Questions:

- What is **Delegatecall** and how does it work in smart contracts?

- Explain how **Oracles** work in the Ethereum ecosystem and provide examples of their usage in smart contracts.

- How can you implement **Upgradable Contracts** using the proxy pattern in Solidity?

- What are the potential risks and challenges in creating smart contracts that interact with multiple other contracts in the blockchain ecosystem?



#### Practical Tasks (Mandatory):

1. Implement a **Crowdfunding** contract that allows users to fund a project with ERC20 tokens using OpenZeppelin's ERC20 library. Ensure that the contract validates whether the project has reached its funding target before funds can be withdrawn.

   - Features: `contribute(uint256 _amount)`, `withdraw()`, and `getFundingStatus()`.

   - **Unit Testing:** Write comprehensive tests for all functionalities, including contribution limits and withdrawal conditions.

   - **Documentation:** Include detailed comments explaining each feature's logic and security considerations.



2. Design a **Decentralized Autonomous Organization (DAO)** system that allows token holders to submit proposals and vote on them using OpenZeppelin's governance libraries.

   - Features: Proposals can include changes to rules or token distribution. Each vote is weighted by token ownership, requiring quorum for approval.

   - **Unit Testing:** Ensure all DAO functionalities work as intended through rigorous testing.

   - **Documentation:** Provide insights into how governance works within your DAO design.



3. Create an upgradable contract system using OpenZeppelin's proxy pattern that allows for future upgrades without losing state or data.

   - Implement functions for upgrading logic while maintaining user data integrity.

   - **Unit Testing:** Write tests to confirm that upgrades do not affect existing data or functionality.

   - **Documentation:** Explain the proxy pattern's advantages for upgradability in your documentation.



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## Submission Instructions



- **Junior:** Submit your smart contract in `.sol` file format via email or GitHub repository along with unit tests and documentation.

- **Middle:** Include a brief description of your approach for both mandatory tasks, unit tests, and documentation explaining your design choices.

- **Senior:** Provide comprehensive documentation on your contract design, including security considerations, gas optimization strategies, unit test coverage, and explanations for each feature implemented.



We expect practical tasks to be completed within 2 to 4 hours. Please also provide explanations for your design choices during implementation.



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Good luck! We look forward to reviewing your work and discussing your solutions further.