The difference between Severity and Priority^[1]

2015-06-24

There are two key things in defects of the software testing. They are:

• Severity
• Priority

What is the difference between Severity and Priority?

Severity: It is the extent to which the defect can affect the software. In other words it defines the impact that a given defect has on the system. 

Severity can be of following types:

• Critical: The defect that results in the termination of the complete system or one or more component of the system and causes extensive corruption of the data. The failed function is unusable and there is no acceptable alternative method to achieve the required results then the severity will be stated as critical.
• Major: The defect that results in the termination of the complete system or one or more component of the system and causes extensive corruption of the data. The failed function is unusable but there exists an acceptable alternative method to achieve the required results then the severity will be stated as major.
• Moderate: The defect that does not result in the termination, but causes the system to produce incorrect, incomplete or inconsistent results then the severity will be stated as moderate.
• Minor: The defect that does not result in the termination and does not damage the usability of the system and the desired results can be easily obtained by working around the defects then the severity is stated as minor.
• Cosmetic: The defect that is related to the enhancement of the system where the changes are related to the look and field of the application then the severity is stated as cosmetic.

Priority: Priority defines the order in which we should resolve a defect. Should we fix it now, or can it wait? This priority status is set by the tester to the developer mentioning the time frame to fix the defect. If high priority is mentioned then the developer has to fix it at the earliest. 

Priority can be of following types:

• Low: The defect is an irritant which should be repaired, but repair can be deferred until after more serious defect have been fixed.
• Medium: The defect should be resolved in the normal course of development activities. It can wait until a new build or version is created.
• High: The defect must be resolved as soon as possible because the defect is affecting the application or the product severely. The system cannot be used until the repair has been done.

Severity and priority are not always one-to-one

• High Priority & High Severity: An error which occurs on the basic functionality of the application and will not allow the user to use the system. (Eg. A site maintaining the student details, on saving record if it, doesn’t allow to save the record then this is high priority and high severity bug.)
• High Priority & Low Severity: The spelling mistakes that happens on the cover page or heading or title of an application.
• High Severity & Low Priority: An error which occurs on the functionality of the application (for which there is no workaround) and will not allow the user to use the system but on click of link which is rarely used by the end user.
• Low Priority and Low Severity: Any cosmetic or spelling issues which is within a paragraph or in the report (Not on cover page, heading, title).

Reference

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