Testing with ethers.js in Blockchain / Solidity - Step-by-Step Execution

Concept Flow - Testing with ethers.js

Write test script

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Setup ethers.js provider and signer

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Deploy or connect to contract

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Call contract functions

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Check results with assertions

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Report pass/fail

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End test

The test script sets up ethers.js, deploys or connects to a contract, calls functions, checks results, and reports success or failure.

Execution Sample

Blockchain / Solidity

import { expect } from 'chai';
import { ethers } from 'hardhat';

describe('SimpleStorage', () => {
  it('stores and retrieves a value', async () => {
    const SimpleStorage = await ethers.getContractFactory('SimpleStorage');
    const storage = await SimpleStorage.deploy();
    await storage.deployed();

    await storage.store(42);
    expect(await storage.retrieve()).to.equal(42n);
  });
});

This test deploys a SimpleStorage contract, stores the number 42, then checks if retrieving returns 42.

Execution Table

Step	Action	Evaluation	Result
1	Import chai and ethers	Modules loaded	Ready to use expect and ethers
2	Get contract factory for SimpleStorage	Factory created	Can deploy contract
3	Deploy SimpleStorage contract	Transaction sent	Contract deployed at address
4	Wait for deployment to complete	Deployment mined	Contract ready
5	Call store(42) on contract	Transaction sent	Value 42 stored
6	Call retrieve() on contract	Returns 42	Value retrieved is 42
7	Assert retrieved value equals 42	Check passes	Test passes
8	Test ends	No errors	Test suite completes successfully

💡 Test ends after assertion passes confirming contract stores and retrieves value correctly

Variable Tracker

Variable	Start	After Step 3	After Step 5	After Step 6	Final
SimpleStorage	undefined	Contract factory object	Contract factory object	Contract factory object	Contract factory object
storage	undefined	Contract instance deployed	Contract instance deployed	Contract instance deployed	Contract instance deployed
storedValue	undefined	undefined	42 stored	42 retrieved	42

Key Moments - 3 Insights

Why do we wait for deployment to complete before calling store()?

Because the contract must be fully deployed on the blockchain before we can interact with it. See step 4 in execution_table where deployment is mined before proceeding.

What happens if the retrieved value does not equal 42?

The assertion in step 7 would fail, causing the test to fail and report an error. This ensures the contract logic is correct.

Why do we use async/await in the test?

Because blockchain calls are asynchronous and we must wait for transactions to complete before checking results, as shown in steps 3, 4, 5, and 6.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of storedValue after step 5?

A undefined

B Contract deployed

C 42 stored

D 42 retrieved

💡 Hint

Check the 'storedValue' row in variable_tracker after step 5

At which step does the test confirm the contract stores the value correctly?

A Step 7

B Step 5

C Step 3

D Step 6

💡 Hint

Look at the assertion step in execution_table where the test passes

If we remove await before storage.store(42), what likely happens?

A Test runs faster and passes

B Test fails because store transaction may not complete before retrieve

C No change, test still passes

D Deployment fails

💡 Hint

Recall why async/await is used in key_moments and steps 5-6 in execution_table

Concept Snapshot

Testing with ethers.js:
- Import ethers and chai for blockchain and assertions
- Deploy or connect to contract asynchronously
- Call contract functions with await
- Use expect() to check results
- Tests pass if assertions succeed
- Async/await ensures correct order of blockchain calls

Full Transcript

This visual execution shows how to test a smart contract using ethers.js. First, the test script imports necessary modules. Then it gets the contract factory and deploys the contract, waiting for deployment to finish. Next, it calls the store function to save a value and waits for the transaction. Then it calls retrieve to get the stored value. Finally, it asserts the retrieved value equals the stored one. The test passes if the assertion succeeds. Variables like the contract instance and stored value change step by step. Key moments include waiting for deployment and using async/await to handle asynchronous blockchain calls. The quiz checks understanding of variable states and test flow.