Priority vs Severity

These two terms are sometimes misunderstand by non-testing-knowledge people. To exactly define the impact of a defect, it should be defined by two attributes which are priority and severity. This is necessary because, for a big project classifying the priority and severity of the defects can be helpful for making decision about the plan for the solving order and finishing testing cycle (exit criteria). In this post, I want to explain priority and severity and how to use it. 
  • Severity: in terms of testing it means that when a defect raises in the system, how severely affects the application and how much user can see the effects of the defect. So the severity is related to the impact of the defect on the system. Generally types of severity are: Minor, Moderate, Major
  • Priority: it is related to customer/bossiness need. It may be used for determination of the order of solving the defects. Defect may has a minor impact on the system but it can be classified as high priority in the requirement document. For example; campaign phone number is entered in a wrong format, this defect can be minor severity but high priority. Generally types of priority are: Low, Medium, High 
When we define the meaning of the defect attributes in the System Test Plan (STP), then impact of a defect can be understand by all the participant. These makes the defect management more applicable. The following are the classical approach for defining the types of severity and priority:
  • Types of Severity:
    • Minor: Defect has very low and local impact on the system. Cosmetic errors, typos in the text, understandable and learnable defects which can be still usable can be set as minor. In some testing tools has Trivial severity level, this should be used for any defect has very low impact.
    • Moderate: Functional defects which has local effect on the system and has alternative way to perform action.
    • Major: Any functional defect which has global effect on the system, harm many point in the system, block the process and don't have alternative way of completion. In some testing tools has Blocker severity level, this should be used for any defect cause service disruption.  
  • Types of Priority:
    • Low: defects which can be as the last items in the list means that they will solve when all other defect has solved. This info can be found in the requirement documents
    • Medium: defects should be solved in a short period of time
    • High: defects must be solved very quickly

Defect prioritization
From the above graphic we can conclude that defects in the hot red color area must be solved quickly but the yellow and gray areas may be ignored for the first release. However the defects in the pink color should be solved after the defects in the red regions.


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