Difference between SMOKE Testing, Sanity Testing & Regression Testing By Shiva sir

  1️⃣ Smoke Testing (Build Verification Testing)

👉 What it is Smoke Testing?

Smoke testing is basic, high-level testing done on a new build to check whether the critical functionalities work and the build is stable enough for detailed testing.

Think of it as:

“Is this build testable or should we reject it immediately?”

👉 When it is done

After new build deployment

Before starting any detailed testing

👉 Who performs it

QA team

Sometimes automation (CI/CD pipelines)

👉 Real-time example

E-commerce Application – New Build

Check only critical flows:

App launches successfully

Login page loads

User can log in

Product list page opens

Add to cart button is visible

❌ If login itself fails → Build is rejected

👉 Importance

✅ Saves QA time

✅ Prevents testing unstable builds

✅ Early defect detection

✅ Protects testing effort

2️⃣ Sanity Testing (Focused Verification)

👉 What it is

Sanity testing is narrow and deep testing done to verify specific changes or bug fixes.

Think of it as:

“Did the specific fix work without breaking related areas?”

👉 When it is done

After minor bug fixes

After small enhancements

Before regression testing

👉 Who performs it

QA team

👉 Real-time example

Bug Fix Scenario

Bug fixed:

“Apply Coupon button was not calculating discount correctly”

Sanity test cases:

Apply valid coupon

Apply expired coupon

Discount calculation

Final amount update

Only related areas are tested, not full application.

👉 Importance

✅ Confirms bug fix quickly

✅ Prevents unnecessary full regression

✅ Faster feedback to developers

✅ Reduces test execution time

3️⃣ Regression Testing (Full Impact Testing)

👉 What it is

Regression testing ensures that new changes have not broken existing functionality.

Think of it as:

“Everything that worked earlier should still work now.”

👉 When it is done

After bug fixes

After new feature implementation

Before release

During maintenance

👉 Who performs it

QA team

Mostly automation testers

👉 Real-time example

Banking Application – New Feature Added

New feature: UPI Payment

Regression test cases:

Login

Balance check

Fund transfer

Bill payment

Transaction history

Logout

Existing payment methods

Even though UPI is new, old features must still work.

👉 Importance

✅ Ensures system stability

✅ Prevents production failures

✅ Protects business-critical flows

✅ Mandatory before release

🔥 Key Differences (Interview-Ready Table)

Feature Smoke Sanity Regression

Purpose Check build stability Verify specific fix Ensure no side effects

Scope Very broad Very narrow Very wide

Depth Shallow Deep Deep

Performed When New build After small change After any change

Time Required Very less Less High

Automation Often automated Mostly manual Mostly automated

Build Rejection Yes No No

📌 Simple Real-Life Analogy

🚗 Car Example

Smoke Testing → Car starts, engine runs

Sanity Testing → Fixed brake issue works correctly

Regression Testing → Lights, AC, steering, brakes still work after repair

🎯 Final Summary (Perfect for Interviews)

Smoke → Is the build stable?

Sanity → Did the fix work?

Regression → Did anything break?

If you want, I can also provide:

✅ Real-time test cases

✅ Automation perspective

✅ QA interview answers

✅ Agile/Scrum usage explanation