Quality is delighting customers
Let me understand you in simple example
You have 100 test cases, Out of 100 test cases 60 cases are passed and 40 are failed. For 40 failed test cases you do re-testing. for 60 passed test cases you do regression testing.
Generally regression testing is being done in three conditions.
1- Environment changes
2- New feature/ functionality added
3- Pass/ Fail Test Cases
4- For stable test cases
We do regression testing to check any impact of bug fix/ new changes in our passed test cases/ in the functionality.
Regression: the act of going back to a previous place or state; return orreversion.
Retest: to test (something) again or differently