If error data is broken into the distinct testing phases of the life cycle (e.g., unit, system, integration), the projected error curve using the SATC model closely fits the rate at which errors are found in each phase.
Some points need to be clarified about the SATC error trend model. The formulation of the SATC equation is the direct result of assuming that at any instant of time, the rate of discovery of errors is proportional to the number of errors remaining in the software and to the resources applied to finding errors. Additional conditions needed in order for the SATC trending model to be a valid are:
The code being tested is not being substantially altered during the testing process, especially through the addition or rework of large amounts of code.
All errors found are reported.
All of the software is tested, and testing of the software is uniform throughout the time of the testing activity.
Condition 1 is present to ensure that the total number of errors is a relatively stable number throughout the testing activity. Conditions 2 and 3 are present to ensure that the estimate of the total number of errors is in fact an estimate of the total errors present in the software at the start of testing - no new errors are introduced during testing. If testing is not "uniform" then the rate of error discovery will not necessarily be proportional to the number of errors remaining in the software and so the equation will not be an appropriate model for errors found. No attempt will be made here to make precise the meaning of the word "uniform".
Some points need to be clarified about the SATC error trend model. The formulation of the SATC equation is the direct result of assuming that at any instant of time, the rate of discovery of errors is proportional to the number of errors remaining in the software and to the resources applied to finding errors. Additional conditions needed in order for the SATC trending model to be a valid are:
The code being tested is not being substantially altered during the testing process, especially through the addition or rework of large amounts of code.
All errors found are reported.
All of the software is tested, and testing of the software is uniform throughout the time of the testing activity.
Condition 1 is present to ensure that the total number of errors is a relatively stable number throughout the testing activity. Conditions 2 and 3 are present to ensure that the estimate of the total number of errors is in fact an estimate of the total errors present in the software at the start of testing - no new errors are introduced during testing. If testing is not "uniform" then the rate of error discovery will not necessarily be proportional to the number of errors remaining in the software and so the equation will not be an appropriate model for errors found. No attempt will be made here to make precise the meaning of the word "uniform".
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