Continuous performance testing means regularly asking: “Can this system stay fast, reliable, and usable when real people use it?”It means running performance tests throughout the software development cycle and after release, rather than testing only once before launch. 

Imagine your production system is a giant black box. Requests go in, responses come out, but you have no idea what’s happening inside. It’s like flying a plane at night with no cockpit instruments. You might be moving forward, but you have no visibility into the altitude, direction, or speed. Without observability, when something goes wrong, you’re essentially walking into that black box blindfolded with your hands outstretched. You can guess, you can poke around, but you’re operating on hunches instead of facts.With observability, the black box turns into a glass box and now you have this x-ray vision so you can find and fix problems before they crash your systems. 

Chaos engineering is the practice of deliberately introducing failures to your system to understand how your system responds to different failures that can manifest to your users. For example, you may want to take down a random API or data service and see the side effect on your users’ applications. If the side effects are impactful and if you have Service Level Agreements (SLA) in place, then this can have a detrimental impact on your organisation.

In its simplest definition, contract testing is used to test that two systems have a shared understanding of expectations. For example, when a web application sends a GET request to a data service, the web application has expectations regarding how the data service should respond. Contract testing captures the interactions between these two systems, which are then stored in a contract that both systems must adhere to.

User stories are short and simple descriptions of a feature or functionality that are told from your user's perspective

In software testing, heuristics are like mental models or shortcuts that we as testers use to guide our work. I like to think of heuristics as strategies that help me generate new ideas on what to test and how to test it especially when I run out of ideas myself. Heuristics are particularly useful when it comes to doing exploratory testing because they give us a guideline on what to explore next. 

A test idea is more about the general thought of what to test in a software. They are often generic and it involves looking at the wider picture.