Codex for Developers: Essentials — Testing Playbook

A focused playbook for testing with Codex. Learners have Codex write unit and edge-case tests from a written pricing policy rather than from the code, diagnose and fix a test that fails only on certain days, and use small deliberate bugs to prove the tests really guard the behaviour. They leave with a repeatable pattern for tests they can trust, not just tests that pass. About 45 minutes including the final.

What this course covers

The course runs across 3 topics, each one a short adaptive session rather than a recorded lecture. The tutor explains the idea, works an example, checks understanding, and adjusts the next step to the answer given.

Writing unit and edge-case tests from the written behaviour — Learners ask Codex for tests based on the policy or spec rather than the code, name the framework and list the boundaries to cover. They ask for the expected value of every case with a reason, check some by hand, and have Codex run the tests.
Diagnosing a failing or flaky test — Give Codex the test, the code and the exact failure and ask for the root cause before any fix. Learners tell a test bug from a code bug and make date-dependent tests deterministic by passing in a fixed date, instead of retrying or skipping them.
Checking that a test really guards the behaviour — A passing test proves little if it would also pass when the code is wrong. Learners spot weak assertions, break one line on purpose to check at least one test fails, and record the test command and testing rules in AGENTS.md.

Skills you build

Results are measured against named skills in the OneRange taxonomy of more than 10,000 skills, so a manager sees proficiency per skill rather than a completion tick.

Who it is for

Software developers. The material is pitched at beginner level, and takes roughly 45 minutes at a typical pace. Because every session adapts, someone who already knows a topic moves through it quickly instead of sitting through an explanation they do not need.

It sits in the Tool: Codex track of the Vero AI Catalog, and can be assigned to one person, a team, or the whole company.

How it is delivered and assessed

Delivery is conversational and interactive, including code lab exercises. There is no video to sit through and no slide deck to click past.

Understanding is checked with a lab assessment of 5 items, with a pass mark of 70%.

Administrators can copy this course into their own library and adapt it — edit the outline, change the duration, swap the assessment format, or ground it in internal documentation so answers cite the company's own source material.

Also in this track

Codex for Everyone: Essentials — Data & Reporting Playbook — A focused playbook for turning a messy spreadsheet export into a simple, repeatable report with Codex, without writing code. Learners clean a copy of the file safely, have Codex build a one-page report, check the numbers against the source by hand, and set it up to re-run next week. About 45 minutes including the final.
Codex for Everyone: Essentials — Internal Tools Playbook — A focused playbook for building a small internal tool with Codex in the ChatGPT desktop app, without writing code. Learners pick a sensible first tool, plan it and let Codex build it on fake data, check every result by hand, and finish with a plain run guide plus a clear sense of when a tool needs an engineer. About 45 minutes including the final.
Codex for Developers: Essentials — Code Review Playbook — A focused playbook for code review with Codex. Learners run /review against a base branch, give Codex a team checklist so it reviews the way the team does, triage its findings into fix, push back and ignore, and see how Codex reviews pull requests on GitHub when a company turns it on. They leave knowing Codex speeds up review but a human still owns the merge. About 45 minutes including the final.
Codex for Everyone: Essentials — Prototypes Playbook — A focused playbook for turning an idea into a clickable prototype with Codex, without writing code. Learners go from a short brief to a working mockup on fake data, refine how it looks by describing changes, gather feedback, and write a clean handoff note so an engineer can tell what is real and what is not. About 45 minutes including the final.
Codex for Developers: Essentials — Refactoring & Migration Playbook — A focused playbook for refactoring and migrating code with Codex without breaking behaviour. Learners pin current behaviour with characterisation tests first, use Plan mode to split a migration into small steps they can each verify, and review every diff before moving on. They leave with a safe, repeatable pattern for changes larger than one function. About 45 minutes including the final.
Codex for Developers Pathway — Use Codex as a daily engineering tool, from your first week to automating engineering for a whole team. Also includes 4 optional playbooks to take any time after Essentials; they don't count toward the certificate.

Frequently asked questions

How long does this course take?

It runs roughly 45 minutes at a typical pace. Because every session adapts, someone who already knows a topic moves through it quickly instead of sitting through an explanation they do not need.

How is it assigned to a team?

An administrator assigns it from the Vero dashboard to one person, a team, a department or the whole company, and sees progress and results per person and per skill.

Can we customise it with our own documents and terminology?

Yes. Administrators can copy this course into their own library and adapt it — edit the outline, change the duration, swap the assessment format, or ground it in internal documentation so answers cite the company's own source material.

Course code TUL-CDX-DEV-121.