The role that pays more than manual QA because it's genuinely engineering — testing skill plus the ability to build the tooling around it.
An SDET — a Software Development Engineer in Test — is a developer whose product is confidence. Instead of clicking through a release checklist, you write the code, infrastructure, and tooling that let a whole team ship without fear. This course covers that job in full: unit tests that isolate one thing and tell you precisely what broke; the three kinds of test doubles and when each is the right lie; integration tests running against real databases in CI; coverage and mutation testing, including why a high coverage number can still mean nothing; how to design code so it's easy to test in the first place; owning the pipeline rather than just feeding it; finding your way around an unfamiliar codebase with blame and bisect; profiling and load testing until you can name the bottleneck; and using AI for generation, impact analysis, and first-pass failure triage. Working code in both Python and TypeScript throughout.
Built by Lakshya Kumar
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Mocks lie about how systems actually connect. Spin up genuine dependencies in CI and test the seams where things really break.
When the real service is slow, costly, or someone else's problem, stand in a believable substitute — without the mock drifting from reality.
100% coverage can still miss every real bug. Set standards the build enforces automatically, and know which numbers are worth chasing.
A thousand tests written without a plan become the reason nobody refactors. Structure yours so changing the code doesn't mean rewriting them.
The moment you're responsible for the build, you're responsible for environments, sharding, and what happens after deploy. Learn all three.
Hard-to-test code is usually badly designed code. Learn the structures — seams, ports, flags, hooks — that make testing straightforward.
Dropped into a repo you've never seen, find the change that caused the bug — and review a pull request in a way developers respect.
Move from 'it feels slow' to naming the exact function, query, or lock responsible — then prove your fix with a repeatable number.
Generate tests at scale, run only the ones a change can affect, and let an AI do the first pass on why a failure happened.
Complete all modules, then submit the required number of capstone projects. Each must earn a passing rating from an admin reviewer.
Fork an open-source project on GitHub that has minimal test coverage (search GitHub for repos with < 20% coverage or no test directory). Add: 20+ unit tests following AAA with proper test doubles, 5+ integration tests using real infrastructure (Testcontainers or in-memory DB), a CI workflow that enforces ≥70% coverage and ≥70% mutation score, and a code quality gate with SonarQube or CodeClimate. Submit a PR to the original project (or your fork) with a description of what you tested and why.
Paste this into any AI chat. Fill in the bracketed parts with your context — you'll get back a straight answer on whether this belongs on your plate.
I'm considering 'SDET & Advanced Engineering' — a course on the full technical depth of Software Development Engineering in Test. Covers: unit testing (AAA, isolation, DI), test doubles (fakes/stubs/mocks), integration testing with Testcontainers, coverage + mutation testing, testable code design, CI/CD quality gates, system design for testability, GitHub/codebase navigation, performance benchmarking, and AI for SDETs. 100 challenges in Python and TypeScript. Context: 1. My current engineering level: [e.g. "junior dev who can write basic tests", "mid-level developer who hasn't focused on testing", "QA engineer who can write Playwright but not unit tests", "experienced SDET learning advanced patterns"] 2. What I can do today: [e.g. "write pytest tests", "use Jest mocks", "nothing beyond clicking", "write API tests but not unit tests"] 3. My goal: [e.g. "get an SDET role at a top tech company", "lead testing at my startup", "bring unit test culture to my team", "move from QA to SWE via the SDET path"] Answer: - Which 2 modules will give me the highest leverage in the next 3 months? - What will I have built by the end that proves SDET-level skills? - Should I do the other QA courses first, or can I jump in here? - What will I NOT be able to do — e.g. "design an entire QA organization", "replace a security engineer", "build custom test frameworks from scratch"?
Implement Pact-style consumer-driven contract testing across 3 microservices. Include the contract repository, the verifier in CI, and a breaking-change blocker on PRs. Demonstrate catching a deliberate breaking API change before merge.
Audit a real test suite for unit/integration/E2E balance. Identify slow flaky E2E tests that could be rewritten as faster integration tests. Rewrite at least 10; measure the suite-runtime delta and the maintenance-cost reduction.
Set up a performance test baseline (k6, Locust, or Gatling) for a critical API. Run nightly; alert on regression beyond 10% from baseline. Demonstrate catching a deliberate slow-query regression.
Build a test-data-management system: factories for test data, fixtures with realistic distributions, data cleanup between runs, ability to reset to a known state in <30s. Document the schema and the workflows it supports.
The canonical reference for test double taxonomy and test design patterns.