Defects Errors lead to defect. Defect lead to failures. When a tester sees an application is not working properly it is bug. When we raise that bug it is defect.To avoid failures we either need to avoid or rectify them. Testing can do both avoidance and rectification.
Error leads to defect. If a defect goes unnoticed it may lead to failure.
Defect can be something like deviation from a standard.
Issues can be missing requirements or extra requirements etc and these can lead to bugs.
Defect can be something that is not supposed to be there like reset button on any page. After user name and password field a Button named Register instead of sign in. Or it can be anything like a missing requirement or extra requirement.
When a system crashes due to these defects it is a failure. Software failure can lead to loss of time, money, business and reputation, injury or death.
Causes of defects can be
Defects are not only found after executing test cases , defects can be even found when we are doing exploratory testing.
When we log a defect in tracking tool like Jira ,gitlab or bugzilla a defect needs to include the following
At the end of the day the qa lead goes through all the defects being raised by different testers and figure out If this defect is valid i.e whether it is actually a defect or is it a duplicate that is being identified by another tester ,And is it defined properly so that it can be reproduced easily. Also one day 1 or 2 of a sprint when maximum bugs pop up it might not be optimal for test lead to go through each and every bug so it the responsibility of the tester that we do our job properly so that we don’t raise any invalid bugs.
Once the defect is fixed by developer it is sent back to the tester who retests this and checks if it is actually fixed or the bug is still there.