What Is The Difference Between Quality Assurance, Quality Control, And Testing?

Many people and organizations are confused about the difference between quality assurance (QA), quality control (QC), and testing. They are closely related, but they are different concepts. Since all three are necessary to effectively manage the risks of developing and maintaining software, it is important for all to understand the differences.

I need to get something straight: QA and QC are different. Why must I point this out? Because programmers don't seem to get it and use these terms interchangeably. While it is usually enough to get your point across with a developer, it is helpful to think about these terms and how they apply to the world of software testing

QA is Quality Assurance  : A set of activities designed to ensure that the development and/or maintenance process is adequate to ensure a system will meet its objectives. , It is a process of verifying predefined requirements for quality. the QC function  involve checking the software against a set of requirements and verifying that the software meets the predefined requirements.

but

QC is Quality Control : A set of activities designed to evaluate a developed work product. It  is much more about providing the continuous and consistent improvement and maintenance of process that enables the QC job. We use the QC process to verify a product does what we think it does, and we use the QA process to give us confidence that the product will meet the needs of customers. To that end the QA process can be considered a meta process that includes aspects of the QC process. It also goes beyond that to influence usability and design, to verify that functionality is not only correct, but useful.

Whereas:

Testing(Tester or Test Engineer) is : The process of executing a system with the intent of finding defects. (Note that the "process of executing a system" includes test planning prior to the execution of the test cases.)

The difference is that QA is process oriented and QC is product oriented.

Testing, therefore is product oriented and thus is in the QC domain. Testing for quality isn't assuring quality, it's controlling it.

Quality Assurance - QA	Quality Control - QC
Quality Assurance makes sure you are doing the right things, the right way	Quality Control makes sure the results of what you've done are what you expected
QA is a failure prevention system that predicts almost everything about product safety, quality standards and legality that could possibly go wrong, and then takes steps to control and prevent flawed products or services from reaching the advanced stages of the supply chain.	QC is a failure detection system that uses a testing technique to identify errors or flaws in products and tests the end products at specified intervals, to ensure that the products or services meet the requirements as defined during the earlier process for QA
QA department develops all the planning processes and procedures in order to try to make sure that the products manufactured or the service delivered by the organization will be of good quality	QC department checks the products or services for defects that happen due to these parameters, trying to achieve the overall QC objective of providing a defect-free product or service to the customers.
QA defines the standards/methodology to be followed in order to meet the customer requirements.	QC ensures that the defined standards are followed at every step
In general, the QA activities are done before the product is manufactured or the service delivered (proactive approach).	The QC activities are done during the manufacturing process and once the product is manufactured
QA tasks are conducted by managers, Leads ,third party auditors, and customers	QC tasks are executed by experts who are directly involved with the design, or manufacture of a product on the shop floor such as engineers, inspectors, etc
- A QA audit would focus on the process elements of a project. e.g.: Are requirements being defined at the proper level of detail? - Process documentation - Establishing standards - Developing checklists - Conducting internal audits	- A QC review will focus on product elements. e.g.: Are the defined requirements the right requirements? - Performing inspections - Performing testing

* For this reason, one person cannot perform both activities (QA and QC) because will result in a conflict of interest.

So to summarize,

QC detected a recurrent problem with the quality of the products. QC provides feedback to QA personnel that there is a problem in the process or system that is causing product quality problems. QA determines the root cause of the problem and then brings changes to the process to ensure that there are no quality issues in future.

Finally,

Both departments are essential to maintain good quality of the deliverable s. And keep in mind no matter how you define QA and QC,  the goal is: to delivery good quality.