In Quality Assurance (QA) testing, both stress testing and load testing are performance testing techniques, but they serve different purposes and simulate different scenarios to assess the system’s behavior and performance.

Load Testing:
Load testing is a type of performance testing that evaluates how a system performs under expected and anticipated normal or peak loads. The main goal of load testing is to determine whether the system can handle the expected user load efficiently and without any significant performance degradation. It helps identify the system’s capacity limits, response times, and potential bottlenecks under different load conditions.
Load testing involves simulating real user traffic by creating virtual users (often referred to as virtual users or virtual clients) and subjecting the system to a load that represents the expected usage pattern. These virtual users send requests to the application, mimicking user behavior and interactions. The load is gradually increased until it reaches the expected maximum, and the system’s performance metrics and response times are measured and analyzed.

Stress Testing:
Stress testing, on the other hand, is a type of performance testing that evaluates the system’s behavior under extreme or beyond-expected load conditions. The main goal of stress testing is to determine the system’s stability, robustness, and responsiveness when it is pushed beyond its maximum capacity.
In stress testing, the load is increased significantly beyond the system’s expected capacity, aiming to identify how it handles the overload and whether it can gracefully recover once the load is reduced. This test helps to uncover potential vulnerabilities, bottlenecks, and weaknesses in the system, which might not be apparent during regular load testing.

Key Differences:
Purpose: Load testing checks how the system performs under expected loads, while stress testing evaluates the system’s behavior under extreme and beyond-expected loads.
Load Level: Load testing involves applying a load that represents anticipated user traffic, while stress testing involves applying a load beyond the system’s capacity.

Focus: Load testing primarily focuses on response times and performance under expected load conditions, while stress testing aims to assess stability and resilience under stressful scenarios.
Testing Environment: Load testing simulates real-world user behavior, whereas stress testing simulates adverse conditions that might occur due to sudden spikes in traffic or other unpredictable events.

Both load testing and stress testing are essential to ensure that a system can handle different usage scenarios effectively and deliver a consistent and satisfactory user experience. It is common to perform both types of tests during the QA process to gain a comprehensive understanding of the system’s performance capabilities.