Q409: Regression Check Drill After Practice Ground UI Upgrades

What Interviewers Want To Evaluate

This drill tests whether you verify existing behavior after improving UI.

Frontend regressions often appear when a seemingly visual change touches state, keyboard behavior, or layout.

The interviewer wants to see a compact but serious regression checklist.

Short Interview Answer

After practice-ground UI upgrades, I would verify that JavaScript and TypeScript samples still run, console output still appears, errors still render, copy controls still work, shortcuts behave correctly, and responsive layouts remain usable. I would also run typecheck and build because the MDX-heavy app relies on static generation.

Regression Surface

Check:

JavaScript page
TypeScript page
run behavior
transpile behavior
worker execution
console capture
copy feedback
keyboard shortcuts
clear console
reset editor
theme toggle
responsive layout

This list is small enough to run after each practice-ground change.

Happy Path

Verify:

open JavaScript practice
run default code
see expected output
copy code
copy console
clear console
reset code

Then repeat the same shape for TypeScript.

Error Path

Use:

throw new Error("test")
console.error("bad path")
while true loop if timeout is safe
invalid TypeScript syntax

The goal is not to break the app for fun.

The goal is to verify recovery.

Keyboard Path

Verify:

Tab indent
Shift Tab outdent
Alt Down duplicate
Ctrl Enter run
Ctrl L clear console
toolbar focus
visible focus ring

Keyboard behavior should not regress during styling changes.

Build Checks

Run:

npm run typecheck
npm run build

The build is especially useful here because new MDX pages and metadata can break static generation.

Common Mistakes

• Testing only the changed button.
• Forgetting TypeScript page behavior.
• Not testing keyboard shortcuts after CSS changes.
• Not checking empty copy states.
• Skipping build because typecheck passed.
• Not checking dark theme contrast.

Final Mental Model

Regression checks are:

small
repeatable
workflow-based
error-aware
keyboard-aware
build-verified

They keep UI polish from becoming product risk.