Defect severity and priority

• Priority of a bug is the urgency of need to fix the bug.
• Severity of a bug is the impact it has on the system. 

Severity
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S1 - Critical: Defect affects critical functionality / data. No workaround.
S2 - Major: Defect affects major functionality / data. Has workaround, but is difficult / complicated.
S3 - Minor: Defect affects minor functionality / non critical.
S4- Low: Does not affect functionality or data. No need for a workaround.
S5 - Cosmetic: Defect affects only the look & feed, but not the functionality.

Priority
---------
P1 -- High: Defect must be fixed ASAP.
P2 -- Medium: Defect can wait until the next build / release.
P3 -- Low: Defect can be deferred until a more serious defect is fixed. 

Airbus - HP Quality Centre 9.2 Central Administration

Software Bug Lifecycle

In TxS, the lifecycle was simple:

1. New
2. Open
3. Assign
4. Fix
5. Reassign
6. Resolved-Closed

V Model - Classical Lifecycle

• Requirements Analysis -- Business requirements document or business requirements specification
• System Design -- Systems requirements specifications / functional specification
• Architecture Design -- High level design
• Module Design - Low-level design

Shift Left (Courtesy BMC)

Shift left is a software testing approach where software testing is performed (moved or shifted) to the left / earlier in the Life-cycle. This basically is "Test Early and Test Often".

• In the Traditional Model, requirements and design happen to the left, and testing of those requirements to the right. As the project progresses, the testing effort increases. 
• Consequently later the defects are found, the costlier it becomes to fix those bugs

• In Shift Left, testing is performed during early stages by engaging early in the project lifecycle.