Difference between Error, Bug, Defect and Failure

Error 
Error occurs when the the human being makes a mistake in code.


Failure
When the code which has got error executed, then the system fails to perform what it should actually perform. Thus, this results to failure


Bug
When the actual result fails to match with the expected result then it is called as bug.

Defect 
If there is is discrepancy in following steps or process, then this results to unexpected behavior then it is defect. 


Hence,
If the programmer does some mistake in coding then it is ERROR,
This ERROR when found by tester is DEFECT,
The DEFECT when accepted by the programmer or developer is called BUG,
And thus, discrepancy between actual result and expected result is called FAILURE.



The failure in program occurs because of several reasons there are bugs in software due to unclear or constantly changing requirements, software complexity, programming errors, timelines, errors in bug tracking, communication gap, documentation errors, deviation from standards etc and many other

Computer Aided Software Testing(CAST)

CAST TOOLS

The acronym stands for "computer Aided software Testing". There are some tools which assist the
testing process

There are various types of CAST tools, some of these are as under:

1. Requirements testing tools support for verification and validation of requirements models

2. Static analysis tools Provide information about the quality of software
and Code is examined, not executed.

3. Test design tools Generate test inputs from a formal specification or CASE repository.

4. Test data preparation tools Data manipulation,selected from existing databases or files,
created according to some rules and edited from other sources.

5. GUI test tool use to test the User interface of the system. for example: selenimum, HP winRunner.

6. Performance test tools simulates realistic load on the system & logs the number of transactions
and response times for selected transactions via user interface.for example Load Runner

7. Dynamic analysis tools Provide run-time information on software (while tests are run)
allocation, use and de-allocation of resources, e.g. memory leaks

8. Debugging tools Used by programmers when investigating, fixing and testing faults.
It is use to find cause of failures.

9. Comparison tools compares the actual results with the expected results.

10. Test management tools does management of test ware, test process, incident managment tool
and traceability

11. Coverage measurement tools Objective measure of what parts of the software structure was executed by tests. Tool reports what has and has not been covered by those tests, line by line and summary statistics.