The software testing is always rounded by three fundamentals terms: Errors, which are something wrong did by a person that produces a problem. Defect is called to difference between the expected results and the actual results. For last, failure is a deviation founded by the end user.
The testing definition are split by two terms, verification mean that the product that we are developing is correct, also known as static testing; and validation correspond to check if the product developed is correct, this term is also called dynamic testing. There are two ways to conduit the testing, first, the positive testing that conducted the application in the positive approach trying to find the things that the system will do. The other way is the negative testing, it´s try to find things that the system will not do.
Conduit to early testing has some benefits very important like minimize cost of fixing defects. Also we can find defects in the requirement specification because sometimes the errors not are in the code.
The most important types of testing are two, the white box testing is applied to the source code and validate that the code is working as expected, this testing are did by the developer team with a technical approach. But, there is a problem, whitey box testing not cover functional areas; this very important requirements are cover by the black box testing, which is developed by test engineers with end-user perception, and validate if the application solves the requirement specification.
For a correct test job it is necessary a test plan. This is a detailed schedule plan with all the activities to do for the software testing; also it includes personal and resources involucrate. This document where did in the first phase of the software testing life cycle, the test planning.
The software testing manual also said that a system developed with 0% of bugs, errors and defects doesn´t exist, it is impossible. You can take an idea from some bugs percent founded in mobile apps: android 17.7%, iphone 18%, ipad 6.6%, BlackBerry 23% and WindowsPhone 16.4%.
This is just an introduction to the software testing; there are more concepts involucrate in this software phase. For more information you can look at: http://www.softwaretestinghelp.com/manual-testing-help-ebook-free-download/