Regression and Performance Testing

Site Admin · 11 Sep 2026 · 7 views

Regression and Performance Testing

Old Bugs Coming Back

A regression is a bug that returns after an unrelated change. The classic story: an upgrade to fix one thing silently breaks another, and no one notices until users complain. Regression testing exists to prove that existing behavior still works after every change.

Regression Testing in Practice

Ideally, regression checking is fully automated: the unit, integration, and end-to-end suites you already maintain are regression tests when they run again after every commit. The key discipline is that every fixed bug produces a new test first, so the failure can never silently return.

@Test
void refundDoesNotDoubleApply() {
    Order o = new Order("O1", 100.0);
    o.refund();
    o.refund();
    assertEquals(0.0, o.total(), 0.001);
}

That test was written when the double-refund bug was found. Running it forever after guards that specific fix.

Performance Testing

Performance testing verifies speed and capacity, and it has its own sub-disciplines:

Load testing: does the system behave at an expected, realistic workload?
Stress testing: how far past the breaking point can it go?
Soak testing: does it hold up under a sustained workload for hours?
Spike testing: does it survive sudden jumps in traffic?

Tools such as JMeter, k6, and Gatling generate scripted load and report response times and error rates.

Baselines and Goals

Performance work needs a goal before a test: a target response time, a throughput, a concurrency level. Test against that target, measure a baseline, then re-run after changes to see the trend. Performance is a curve, not a pass/fail, and without a recorded baseline you cannot tell whether the last deploy helped or hurt.