Hardhat testing setup in Blockchain / Solidity - Time & Space Complexity

Time Complexity: Hardhat testing setup

O(n)

Understanding Time Complexity

When running tests with Hardhat, it's important to understand how the time taken grows as the number of tests or contracts increases.

We want to know how the testing time changes when we add more test cases or contracts.

Scenario Under Consideration

Analyze the time complexity of the following Hardhat test setup code.

const { expect } = require("chai");
describe("Token contract", function () {
  let Token, token, owner, addr1;

  beforeEach(async function () {
    Token = await ethers.getContractFactory("Token");
    token = await Token.deploy();
    [owner, addr1] = await ethers.getSigners();
  });

  it("Should assign total supply to owner", async function () {
    const ownerBalance = await token.balanceOf(owner.address);
    expect(await token.totalSupply()).to.equal(ownerBalance);
  });
});
    

This code sets up a test for a token contract, deploying it before each test and checking balances.

Identify Repeating Operations

Identify the loops, recursion, array traversals that repeat.

• Primary operation: The beforeEach hook runs before every test, redeploying the contract.
• How many times: Once per test case inside the describe block.

How Execution Grows With Input

As the number of test cases grows, the setup runs before each one, increasing total time.

Input Size (number of tests)	Approx. Operations (deployments)
10	10 deployments
100	100 deployments
1000	1000 deployments

Pattern observation: The total setup time grows directly with the number of tests.

Final Time Complexity

Time Complexity: O(n)

This means the total testing time grows in a straight line as you add more tests.

Common Mistake

[X] Wrong: "Running more tests won't affect setup time much because deployment is fast."

[OK] Correct: Each test runs the setup separately, so deployment time adds up and grows with the number of tests.

Interview Connect

Understanding how test setup time grows helps you write efficient tests and shows you can think about performance in real projects.

Self-Check

What if we moved the contract deployment from beforeEach to before? How would the time complexity change?

Practice

1. What is the main purpose of using Hardhat testing setup in blockchain development?

easy

A. To create user interfaces for blockchain applications

B. To deploy smart contracts directly to the main Ethereum network

C. To write and run tests for smart contracts on a local blockchain

D. To mine real cryptocurrency coins

Solution

1. Step 1: Understand Hardhat testing role

   Hardhat testing setup is designed to help developers write and run tests for smart contracts safely.

2. Step 2: Identify the environment used

   Tests run on a local blockchain, which means no real money or main network is involved.

3. Final Answer:

   To write and run tests for smart contracts on a local blockchain -> Option C

4. Quick Check:

   Hardhat testing = local smart contract tests [OK]

Hint: Hardhat tests run locally, not on mainnet [OK]

Common Mistakes:

• Confusing testing with deployment to mainnet
• Thinking Hardhat mines real coins
• Assuming Hardhat builds user interfaces

2. Which of the following is the correct way to start a test suite in Hardhat using Mocha?

easy

A. test('MyContract', function() { ... })

B. describe('MyContract', function() { ... })

C. suite('MyContract', () => { ... })

D. context('MyContract', function() { ... })

Solution

1. Step 1: Recall Mocha test structure

   Hardhat uses Mocha for testing, which organizes tests with describe blocks.

2. Step 2: Identify correct syntax

   The describe function takes a string and a callback function to group tests.

3. Final Answer:

   describe('MyContract', function() { ... }) -> Option B

4. Quick Check:

   Mocha test suites use describe() [OK]

Hint: Use describe() to group tests in Hardhat [OK]

Common Mistakes:

• Using test() instead of describe() for suites
• Confusing suite() or context() with Mocha syntax
• Missing function keyword or arrow function

3. Given this Hardhat test snippet, what will be the output when running the test?

describe('SimpleTest', function() {
  it('should return true', async function() {
    const result = true;
    console.log(result);
    expect(result).to.equal(true);
  });
});

medium

A. true and test passes

B. false and test fails

C. undefined and test passes

D. Error: expect is not defined

Solution

1. Step 1: Analyze console output

   The code logs the variable result which is set to true, so console shows 'true'.

2. Step 2: Check assertion

   The test asserts result equals true, which is correct, so test passes.

3. Final Answer:

   true and test passes -> Option A

4. Quick Check:

   console.log(true) + expect(true) passes [OK]

Hint: Check console.log and expect values carefully [OK]

Common Mistakes:

• Assuming expect is undefined without import
• Confusing console output with test result
• Thinking test fails because of async function

4. Identify the error in this Hardhat test code snippet:

describe('Token', function() {
  it('should deploy contract', async () => {
    this.timeout(20000);
    const Token = await ethers.getContractFactory('Token');
    const token = await Token.deploy();
    await token.waitForDeployment();
    expect(token.address).to.be.a('string');
  });
});

medium

A. Missing import of ethers from Hardhat

B. deploy() should not be awaited

C. Incorrect assertion method for address type

D. Using arrow function in it() causes context loss

Solution

1. Step 1: Check function style in it()

   Using arrow functions in Mocha's it blocks can cause loss of this context, which Hardhat sometimes relies on.

2. Step 2: Verify other parts

   Imports and await usage are correct; assertion syntax is valid for checking string type.

3. Final Answer:

   Using arrow function in it() causes context loss -> Option D

4. Quick Check:

   Use function() not arrow in it() [OK]

Hint: Avoid arrow functions in it() blocks [OK]

Common Mistakes:

• Ignoring context loss with arrow functions
• Thinking deploy() is synchronous
• Assuming ethers import is automatic

5. You want to test a smart contract function that transfers tokens and emits an event. Which setup correctly tests the event emission using Hardhat and Chai?

hard

A. await expect(token.transfer(addr1.address, 100)).to.emit(token, 'Transfer').withArgs(owner.address, addr1.address, 100);

B. expect(token.transfer(addr1.address, 100)).to.emit('Transfer').withArgs(owner.address, addr1.address, 100);

C. await token.transfer(addr1.address, 100); expect(token).to.emit('Transfer');

D. token.transfer(addr1.address, 100); expect(token).to.emit(token, 'Transfer');

Solution

1. Step 1: Understand event testing syntax

   Hardhat with Chai uses await expect(transaction).to.emit(contract, eventName).withArgs(...) to test events.

2. Step 2: Check options for correct usage

   await expect(token.transfer(addr1.address, 100)).to.emit(token, 'Transfer').withArgs(owner.address, addr1.address, 100); correctly awaits the transaction and specifies contract and event with arguments.

3. Step 3: Identify errors in other options

   The other options either miss the await before expect, fail to specify the contract instance in to.emit(), or use incorrect syntax chaining.

4. Final Answer:

   await expect(token.transfer(addr1.address, 100)).to.emit(token, 'Transfer').withArgs(owner.address, addr1.address, 100); -> Option A

5. Quick Check:

   Use await expect(...).to.emit(contract, event) [OK]

Hint: Always await expect() when testing events [OK]

Common Mistakes:

• Forgetting to await the expect call
• Not specifying the contract in to.emit()
• Calling expect on transaction result instead of promise