Writing test cases in Blockchain / Solidity - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main purpose of writing test cases in blockchain development?

To verify that smart contracts and blockchain applications work correctly and securely before deployment.

beginner

Name one common framework used for writing test cases in Ethereum smart contracts.

Truffle is a popular framework that helps write, run, and manage test cases for Ethereum smart contracts.

intermediate

Why should test cases cover edge cases in blockchain applications?

Because blockchain transactions are irreversible, catching unusual or rare scenarios early prevents costly mistakes.

beginner

What does a unit test focus on in blockchain smart contract testing?

It tests a small part or function of the smart contract independently to ensure it behaves as expected.

intermediate

How can automated test cases improve blockchain development?

They save time by running tests quickly and repeatedly, helping catch bugs early and ensuring code quality.

Which of the following is a key reason to write test cases for blockchain smart contracts?

A To ensure the contract behaves correctly before deployment

B To make the contract run faster

C To increase the contract size

D To avoid writing documentation

Test cases help verify that smart contracts work correctly and securely before they are deployed.

What type of test checks a single function in a smart contract?

A Performance test

B Integration test

C System test

D Unit test

Unit tests focus on testing individual functions or parts of the contract independently.

Which framework is commonly used for testing Ethereum smart contracts?

A React

B Django

C Truffle

D Angular

Truffle is a popular framework designed for Ethereum smart contract development and testing.

Why is it important to test edge cases in blockchain applications?

A Because blockchain transactions can be reversed easily

B Because blockchain transactions are irreversible and errors can be costly

C Because edge cases improve UI design

D Because edge cases are the most common scenarios

Irreversible blockchain transactions mean catching rare or unusual cases early is critical to avoid costly mistakes.

How do automated test cases benefit blockchain development?

A They save time and catch bugs early

B They require manual checking

C They slow down deployment

D They increase gas fees

Automated tests run quickly and repeatedly, helping developers find bugs early and maintain code quality.

Explain why writing test cases is crucial in blockchain smart contract development.

Think about what happens if a smart contract has a bug after deployment.

Describe the difference between unit tests and integration tests in blockchain testing.

Consider testing one piece versus testing how pieces work together.

Practice

1. What is the main purpose of writing test cases for blockchain smart contracts?

easy

A. To find and fix errors before deploying the contract

B. To make the contract run faster on the blockchain

C. To increase the contract's gas cost

D. To make the contract code longer

Solution

1. Step 1: Understand the role of test cases

   Test cases are written to check if the code works correctly and to catch mistakes early.

2. Step 2: Relate to blockchain deployment

   Since blockchain contracts are hard to change after deployment, testing helps avoid costly errors.

3. Final Answer:

   To find and fix errors before deploying the contract -> Option A

4. Quick Check:

   Test cases catch errors early = C [OK]

Hint: Test cases catch errors before deployment [OK]

Common Mistakes:

• Thinking tests speed up contract execution
• Believing tests increase gas cost intentionally
• Assuming tests make code longer for no reason

2. Which of the following is the correct syntax to group tests in a blockchain testing framework like Mocha?

easy

A. itGroup('Token tests', () => { /* tests */ })

B. group('Token tests', () => { /* tests */ })

C. testGroup('Token tests', () => { /* tests */ })

D. describe('Token tests', () => { /* tests */ })

Solution

1. Step 1: Recall common test grouping syntax

   In Mocha and similar frameworks, describe is used to group related tests.

2. Step 2: Identify correct function name

   Only describe is the standard function for grouping; others are incorrect or do not exist.

3. Final Answer:

   describe('Token tests', () => { /* tests */ }) -> Option D

4. Quick Check:

   Group tests with describe() = A [OK]

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

Common Mistakes:

• Using group() instead of describe()
• Confusing it() with describe()
• Inventing non-existent functions like testGroup()

3. Consider this test case snippet for a smart contract function that stores a value:

it('should store the value correctly', async () => {
  await contract.store(42);
  const result = await contract.retrieve();
  assert.equal(result.toNumber(), 42);
});

What will be the output if the contract stores 42 correctly?

medium

A. Test passes with no errors

B. Test fails with assertion error

C. Syntax error in test code

D. Runtime error due to missing function

Solution

1. Step 1: Analyze the test steps

   The test calls store(42) then retrieves the value and checks if it equals 42.

2. Step 2: Understand assertion behavior

   If the contract works correctly, result.toNumber() will be 42, so assert.equal passes without error.

3. Final Answer:

   Test passes with no errors -> Option A

4. Quick Check:

   Correct value stored means test passes = A [OK]

Hint: If assert matches expected, test passes [OK]

Common Mistakes:

• Assuming test fails even if values match
• Confusing syntax errors with assertion failures
• Ignoring async/await usage in tests

4. Identify the error in this test case for transferring tokens:

it('should transfer tokens', async () => {
  await contract.transfer(receiver, 100);
  const balance = await contract.balanceOf(receiver);
  assert.equal(balance, 100);
});

medium

A. Missing await before balanceOf call

B. No error, test is correct

C. Incorrect assertion comparing balance object to number

D. transfer function called without sender address

Solution

1. Step 1: Check async calls and returns

   The balanceOf likely returns a BigNumber object, not a plain number.

2. Step 2: Verify assertion correctness

   Comparing balance directly to 100 fails because types differ; conversion to number is needed.

3. Final Answer:

   Incorrect assertion comparing balance object to number -> Option C

4. Quick Check:

   Compare values with matching types = D [OK]

Hint: Convert BigNumber to number before assert [OK]

Common Mistakes:

• Forgetting to convert BigNumber to number
• Assuming balanceOf returns a plain number
• Missing await on async calls

5. You want to write a test case that checks if a smart contract correctly rejects unauthorized users from changing the owner. Which approach is best?

hard

A. Call the changeOwner function from the owner account and expect success

B. Call the changeOwner function from an unauthorized account and expect an error

C. Call the changeOwner function without any account specified

D. Skip testing unauthorized access because it is handled by blockchain

Solution

1. Step 1: Understand test goal

   The test should verify that unauthorized users cannot change ownership.

2. Step 2: Choose test action

   Calling changeOwner from a non-owner account and expecting an error confirms access control works.

3. Step 3: Eliminate wrong options

   Testing with owner account or no account does not check unauthorized rejection; skipping test misses bugs.

4. Final Answer:

   Call the changeOwner function from an unauthorized account and expect an error -> Option B

5. Quick Check:

   Test unauthorized access by expecting failure = B [OK]

Hint: Test unauthorized calls expect errors [OK]

Common Mistakes:

• Testing only authorized calls
• Ignoring unauthorized access tests
• Assuming blockchain prevents all unauthorized actions