Overview
What this challenge is about.
Write JUnit 5 tests to kill 30+ mutants in a travel pricing module and earn a verifiable certificate.
The scenario
TravelStack serves mid-market travel agencies whose margins live or die on correct fares, multi-currency conversion, and agency commissions; a single wrong rounding rule or stale discount tier can over- or under-charge hundreds of bookings before anyone notices.
The Brief
What you'll do, and what you'll demonstrate.
Find where 91 percent line coverage hides ineffective tests and close that gap on the five highest-stakes pricing classes by killing surviving mutants.
Earning criteria — what you'll demonstrate
- Explain why line coverage overstates test effectiveness and how mutation testing measures what coverage cannot
- Configure and run PIT against a Java service and interpret per-class mutation scores
- Prioritize testing effort by business risk rather than by easiest wins
- Write targeted JUnit 5 assertions that kill specific surviving mutants while keeping tests readable
- Reason about the operational trade-offs of enforcing a mutation-score gate in continuous integration
Program Fit
Where this fits in your program.
Sharpens the same skills your degree expects you to demonstrate.
Aligned coursework coming soon.
Skills
Skills you'll demonstrate.
Each one shows up on your verified credential.
- Mutation Testing
Apply mutation testing to solve real industry problems and demonstrate production-level capability.
- Java
Apply java to solve real industry problems and demonstrate production-level capability.
- Junit
Apply junit to solve real industry problems and demonstrate production-level capability.
- Code Coverage
Apply code coverage to solve real industry problems and demonstrate production-level capability.
- Test Strategy
Apply test strategy to solve real industry problems and demonstrate production-level capability.
- Ci Cd
Apply ci cd to solve real industry problems and demonstrate production-level capability.
Careers
Career paths this challenge builds toward
Completing this challenge demonstrates skills that transfer directly to these roles:
Software Engineer in Test
This challenge builds the core habit of judging tests by what they catch, not what they run. You leave able to measure test effectiveness, target the riskiest code, and defend testing investment with hard numbers — the daily work of an engineer who owns quality.
This challenge sharpens
- mutation-testing
- junit
- test-strategy
Backend Java Engineer
Pricing logic is exactly the high-stakes backend code where silent bugs cost money. Practicing PIT on a Java service teaches you to ship business-critical code with tests that genuinely protect it, a skill backend teams value highly.
This challenge sharpens
- java
- mutation-testing
- code-coverage
Build and Release Engineer
Deciding whether to gate builds on a mutation-score threshold is a real release-engineering trade-off between safety and speed. You finish able to weigh quality gates against build-time cost and recommend pipeline policy with evidence.
This challenge sharpens
- ci-cd
- mutation-testing
- test-strategy