Testing can never completely identify all the defects within any software. Instead, it furnishes a criticism or comparison that compares the state and behaviour of the products.
A primary purpose of testing is to detect software failures, so that defects may be discovered and corrected. Testing cannot establish that a product functions properly under all conditions but can only establish that it does not function properly under specific conditions.
The scope of software testing often includes examination of code as well as execution of that code in various environments and conditions as well as examining the aspects of code: does it do what it is supposed to do and what it needs to do
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