01 A correct value can hide a wrong state
“verifying the quality, structure, and intention of code” (opens the source)
Check what the code changes, as well as what it returns.
Coding interview prep in an AI-native world
Trace the code, find a counterexample and choose a test that exposes it.
Trace the cachePractice interviews
02 Make the broken promise precise
“often not following essential invariants of the codebase” (opens the source)
A counterexample ties the defect to a stated contract.
03 Find the schedule that exposes the defect
“Form a hypothesis before changing things.” (opens the source)
Predict the state before changing the callback.
04 Input chunks are not complete records
“programs that function as described in the task sheet” (opens the source)
Define completion and EOF before choosing the parser repair.
05 Test the whole result, not one rounded share
“consider various trade-offs and edge cases” (opens the source)
Check conservation, zero input and the stated tie rule.
Finite tests need an honest coverage limit.
Sources
- Matthew Saffer, Author; works on distributed systems infrastructure and productivity tooling, at the time. Jane Street Blog, “Our software engineering interviews are changing (a little)”, Nov 2, 2026. Open the source. Checked against the published text.
- Yaron Minsky, Author, Jane Street engineering essay, at the time. Jane Street Blog, “Formal methods and the future of programming”, Jun 7, 2026. Open the source. Checked against the published text.
- PostHog, Engineering candidate guide, at the time. PostHog Handbook, “Preparing for the engineering SuperDay”, Undated. Open the source. Checked against the published text.
- Suhail Patel, Principal Engineer, at the time. Monzo Technology, “Demystifying the Backend Engineering interview process”, Mar 1, 2025. Open the source. Checked against the published text.
- Wise, Backend engineering pair-interview guide, at the time. Wise Careers, “Backend Pair Programming Interviews”, Undated. Open the source. Checked against the published text.
Last reviewed Nov 10, 2026