Software Testing Metrics

Metrics are the most important responsibility of the Test Team. Metrics allow for deeper understanding of the performance of the application and its behavior. The fine tuning of the application can be enhanced only with metrics. In a typical QA process, there are many metrics which provide information.

The following can be regarded as the fundamental metric:

1. Functional or Test Coverage Metrics.

2. Software Release Metrics.

3. Software Maturity Metrics.

4. Reliability Metrics.

•          Mean Time To First Failure (MTTFF).
•          Mean Time Between Failures (MTBF).
•          Mean Time To Repair (MTTR).

1. Functional or Test Coverage Metric:

It can be used to measure test coverage prior to software delivery. It provides a measure of the percentage of the software tested at any point during testing.

It is calculated as follows:

Function Test Coverage = FE/FT

Where, 

FE -  is the number of test requirements that are covered by test cases that were executed against 

the software

FT - is the total number of test requirements

2. Software Release Metrics:

The software is ready for release when:

    1. It has been tested with a test suite that provides 100% functional coverage, 80% branch coverage, and 100% procedure coverage.

    2. There are no level 1 or 2 severity defects.

    3. The defect finding rate is less than 40 new defects per 1000 hours of testing

    Stress testing, configuration testing, installation testing, Naive user testing, usability testing,

    and sanity testing have been completed

3. Software Maturity Metric :

Software Maturity Index is that which can be used to determine the readiness for release of a software system. This index is especially useful for assessing release readiness when changes, additions, or deletions are made to existing software systems. It also provides an historical index of the impact of changes. It is calculated as follows:

SMI = Mt - ( Fa + Fc + Fd)/Mt.

Where

SMI - is the Software Maturity Index value

Mt - is the number of software functions/modules in the current release

Fc - is the number of functions/modules that contain changes from the previous release

Fa  - is the number of functions/modules that contain additions to the previous release

Fd - is the number of functions/modules that are deleted from the previous release

4. Reliability Metrics:

Reliability is calculated as follows:

Reliability = 1 - Number of errors (actual or predicted)/Total number of lines of executable code

This reliability value is calculated for the number of errors during a specified time interval.

Three other metrics can be calculated during extended testing or after the system is in production. 

They are:

MTTFF (Mean Time to First Failure)

MTTFF = The number of time intervals the system is operable until its first failure (functional failure only).

MTBF (Mean Time Between Failures)

MTBF = Sum of the time intervals the system is operable

MTTR (Mean Time To Repair)

MTTR = sum of the time intervals required to repair the system