Writing test cases in Node.js - Step-by-Step Execution

Concept Flow - Writing test cases

Write test function

↓

Set up inputs

↓

Call function under test

↓

Check output vs expected

↓

Pass or Fail result

↓

Repeat for other cases

↓

Run all tests and report

This flow shows how to write a test: prepare inputs, run the code, check results, and report pass or fail.

Execution Sample

Node.js

const assert = require('assert');

function add(a, b) {
  return a + b;
}

let a = 2;
let b = 3;
let result = add(a, b);
assert.strictEqual(result, 5);

This code tests if the add function returns 5 when given 2 and 3.

Execution Table

Step	Action	Input	Function Call	Expected Output	Actual Output	Test Result
1	Call add	2, 3	add(2, 3)	5	5	Pass
2	Check equality	N/A	N/A	5	5	Pass
3	End tests	N/A	N/A	N/A	N/A	All tests passed

💡 All test cases executed and passed successfully.

Variable Tracker

Variable	Start	After Test 1	Final
a	undefined	2	2
b	undefined	3	3
result	undefined	5	5

Key Moments - 2 Insights

Why do we compare actual output to expected output?

Comparing actual to expected output (see execution_table step 2) confirms if the function works correctly.

What happens if the test fails?

If actual output differs from expected, the test fails and reports an error instead of 'Pass' (not shown here but would stop or log failure).

Visual Quiz - 3 Questions

Look at the execution table, what is the actual output of add(2, 3)?

A 5

B 2

C 3

D undefined

💡 Hint

Check the 'Actual Output' column in step 1 of the execution_table.

At which step do we verify if the test passes or fails?

A Step 1

B Step 3

C Step 2

D No verification step

💡 Hint

Look at the 'Test Result' column in the execution_table.

If add(2, 3) returned 6, how would the test result change in the table?

A Test Result would be 'Pass'

B Test Result would be 'Fail'

C No change

D Test would be skipped

💡 Hint

Compare expected vs actual output in execution_table step 1.

Concept Snapshot

Writing test cases in Node.js:
- Require assert module
- Write a test function
- Call function with inputs
- Use assert.strictEqual(actual, expected)
- Run tests to see pass/fail
- Repeat for multiple cases

Full Transcript

Writing test cases means checking if your code works as expected. You write a test function, give it inputs, run your code, and compare the output to what you expect. If they match, the test passes. If not, it fails and shows an error. This helps catch mistakes early. In Node.js, you can use the assert module to do this simply. The example shows testing an add function with inputs 2 and 3, expecting 5. The test passes because the actual output matches expected. This process repeats for all test cases to ensure your code is reliable.