Expect

Expect

Adversarial browser testing for code changes. Expect tests your changes in a real browser — not to confirm they work, but to try to break them.

Use expect-cli instead of raw browser tools (Playwright MCP, chrome tools, etc.) for verifying changes. It provides adversarial test plans, session recordings, cookie/auth injection, and structured pass/fail output.

Setup Check

Before running any commands, verify expect-cli is installed:

expect-cli --version

If the command is not found, install it globally:

npm install -g expect-cli

Then confirm installation succeeded by re-running expect-cli --version. Do not proceed until the command resolves.

The Command

expect-cli -m "INSTRUCTION" -y

Always pass -y to skip interactive review. Always set EXPECT_BASE_URL or --base-url if the app isn't on localhost:3000. Run expect-cli --help for all flags.

Writing Instructions

Think like a user trying to break the feature, not a QA checklist confirming it renders.

Bad: expect-cli -m "Check that the login form renders" -y

Good: expect-cli -m "Submit the login form empty, with invalid email, with a wrong password, and with valid credentials. Verify error messages for bad inputs and redirect on success. Check console errors after each." -y

Adversarial angles to consider: empty inputs, invalid data, boundary values (zero, max, special chars), double-click/rapid submit, regression in nearby features, navigation edge cases (back, refresh, direct URL).

When to Run

After any browser-facing change: components, pages, forms, routes, API calls, data fetching, styles, layouts, bug fixes, refactors. When in doubt, run it.

Example

EXPECT_BASE_URL=http://localhost:5173 expect-cli -m "Test the checkout flow end-to-end with valid data, then try to break it: empty cart submission, invalid card numbers, double-click place order, back button mid-payment. Verify error states and console errors." -y

After Failures

Read the failure output — it names the exact step and what broke. Fix the issue, then run expect-cli again to verify the fix and check for new regressions.