[ISTQB] 1.1 Why is Testing Necessary? (K2)

LO-1.1.3 Give reasons why testing is necessary by giving examples (K2)

Testing is a part of software quality assessment.Testing should make sure that the software sticks to:

• its specification,
• what is expected by stakeholders, 
• what's needed by final users. 

However, "test all the code or software" is impossible so we have to assess risks, understand and prioritize software requirements for building the most efficient test strategy and coverage. 

LO-1.1.4 Describe why testing is part of quality assurance and give examples of how testing contributes to higher quality (K2)

There is a standard definition of quality given by ISTQB (see below) but also some examples showing that quality assurance is a subjective notion depending on product/software context and people's opinion and expectations.

But the main principles to keep in mind are that testing contributes:
- to measure quality and should increase it (measured by number of defects found and fixed).
- to ensure that acceptance criteria defined beforehand with the stakeholders are met. 

Quality assurance and testing activities are part of quality management and have to take in account "risks and costs associated with the project".

LO-1.1.5 Explain and compare the terms error, defect, fault, failure and the corresponding terms mistake and bug, using examples (K2)

• quality: Degree to which a component system or process meets specified requirements and/or user/customer needs and expectations.

• error / mistake: A human action that produces an incorrect result.

• defect / bug / fault: A flaw in a component or system that can cause the component or system to fail to perform its required function, e.g an incorrect statement or data definition. A defect, if encountered during execution, may cause a failure of the component or system.

• failure: Deviations of the component or system from its expected delivery service or result. Deviations may be caused by human incorrectly the software but also by environmental conditions (pollution, temperature, radiation burst).