Load Testing
Load testing is a type of performance testing that evaluates how a system performs under expected or anticipated workload conditions.
“A type of performance testing conducted to evaluate the behavior of a component or system under varying loads, usually between anticipated conditions of low, typical, and peak usage.”
(Definition reproduced from the ISTQB Glossary. Copyright belongs to ISTQB.)
View the complete ISTQB GlossaryWhat is Load Testing?
The objective is to verify that response times, throughput, and resource utilization meet performance requirements while the system handles normal or peak expected loads.
Expected workload: Tests are performed within planned operating limits.
Performance measurement: Response time, throughput, and resource usage are monitored.
Business confidence: Confirms readiness for anticipated production traffic.
Real World Example
A ticketing platform expects around 500 concurrent users on a normal day, and up to 5,000 during the on-sale moment for a major concert.
The team has only ever clicked through the checkout manually with a handful of people in the room, so nobody actually knows how response times behave as concurrent users climb from a typical day toward that anticipated peak.
The tester simulates the specific range the business expects: 500 users, then 2,500, then the full 5,000, measuring response time, error rate, and resource usage at each step — deliberately staying within the anticipated low-to-peak range rather than pushing past it to find a breaking point.
Checkout response times are found to degrade sharply at 3,000 concurrent users, well before the anticipated peak of 5,000 — giving the team time to fix a database connection pool limit before the real event, exactly the kind of finding Load testing across the expected usage range is meant to surface.
Practice Questions
Question 1
A ticketing platform expects up to 5,000 concurrent users during a peak on-sale event. A tester simulates 500, then 2,500, then 5,000 concurrent users, measuring response time and errors at each step. Which type of testing is this?
Question 2
A team wants to know how their checkout service performs specifically within the range of usage they actually expect in production, from quiet periods to their busiest anticipated peak. Which testing type MOST directly answers this?
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