Writing test cases in Blockchain / Solidity - Step-by-Step Execution

Concept Flow - Writing test cases

Identify feature to test

↓

Write test case: inputs, expected output

↓

Run test case

↓

Compare actual vs expected

↓

Confirm code

↓

Repeat

This flow shows how to write and run test cases to check if blockchain code works as expected.

Execution Sample

Blockchain / Solidity

function testTransfer() {
  let balanceBefore = getBalance(user);
  transfer(user, 10);
  let balanceAfter = getBalance(user);
  assert(balanceAfter === balanceBefore - 10);
}

A simple test case checking if transferring 10 tokens reduces user's balance by 10.

Execution Table

Step	Action	Value/Check	Result
1	Get balanceBefore	balanceBefore = 100	Stored 100
2	Call transfer(user, 10)	Balance reduces by 10	Transfer done
3	Get balanceAfter	balanceAfter = 90	Stored 90
4	Assert balanceAfter === balanceBefore - 10	90 === 100 - 10	True, test passes

💡 Test ends after assertion passes confirming transfer works correctly

Variable Tracker

Variable	Start	After Step 1	After Step 3	Final
balanceBefore	undefined	100	100	100
balanceAfter	undefined	undefined	90	90

Key Moments - 2 Insights

Why do we check balanceBefore before transfer?

We need the original balance to compare after transfer. See execution_table step 1 and 3 where balanceBefore and balanceAfter are stored.

What if the assertion fails?

If assertion fails (step 4), it means transfer did not reduce balance correctly. We must fix code or test before continuing.

Visual Quiz - 3 Questions

Look at the execution table, what is balanceAfter at step 3?

A 10

B 90

C 100

D Undefined

💡 Hint

Check the 'Value/Check' column at step 3 in execution_table

At which step do we confirm the test passes?

A Step 1

B Step 2

C Step 4

D Step 3

💡 Hint

Look at the 'Result' column for the step where assertion is checked

If transfer did not reduce balance, which step would fail?

A Step 4

B Step 1

C Step 2

D Step 3

💡 Hint

Assertion check in step 4 compares expected and actual balances

Concept Snapshot

Writing test cases:
1. Identify feature to test.
2. Write test with inputs and expected output.
3. Run test and capture actual output.
4. Compare actual vs expected.
5. Pass means code works; fail means fix needed.
Repeat for confidence.

Full Transcript

Writing test cases in blockchain means checking if code works as expected. First, pick what to test. Then write a test case with inputs and what you expect to happen. Run the test and get actual results. Compare actual results with expected. If they match, test passes. If not, fix code or test. Repeat this process to make sure your blockchain code is correct and safe.