Problem:
Predicting amount of defects in the week to come is difficult.
Being able
to guess the amount of defects found in the week(s) to come is very useful for ressource
estimation, risk evaluation and other test managment related activities. Furthermore
this require a little crystal ball technology, as it requires the test manager
to make a qualified quess, based on assumptions related to the test items and
resources.
Solution:
Use your defects trends as guide for the estimation.
Being able
to make qualified guesswork require that you use your metrics as foundation for
seeing trends. The low-tech approach that I use is to extrapolate the trend and
see where total will be end of next week and the week after. The cool thing
about low tech solutions is that they are easily applied and communicated,
Consider
this example, where test has been running for 2 weeks and question from
development team is how much effort shall we reserve for bug-fixing. This
question is in fact: “How many defects should we expect raised next week?”
Using the
low tech approach I just draw a line that follows the trend from the previous
weeks of testing. That gives an indication on where the defect count will end
if all test conditions are the same.
The
following factors can should then be taken into account before guessing the
total defects next week:
These
assumptions are then used to adjust the slope of the trendline that you base
your guesstimate. In above example the trendline is set higher than average, as
the test items in week 3 are highly complex and 1st time under test. This lands
the defect total on 85+, or additional 35 defects in week 3 (calculated as week
3 total minus week 2 total).
You can
also estimate severity for the defects to come in the following way: Combine
your trend graph with your defects severity trends then you can add severity as
a flavor to the estimate. In above example project we have the following
severity distribution after week 2: 7% Critical 13% Major 25% Medium 37% Minor
and 18% Cosmetic. This leaves week 3’s 35 estimated defects with the following
spread: 2,5 Critical 4,5 Major 8,75
Medium 13 Minor and 6,25 Cosmetic
There is no
rocket science in the equation, but only simple logic based on extrapolation of
trends that is easily communicated to the recipient. Putting the graph with trend
line and your assumptions in a mail is a short route to setting expectations. There
are also other situations where this approach will come in handy, when
communicating general quality trend in a delivery or when talking to customers
or steering committees while doing expectation management.
Happy
testing & Enjoy your weekend!
/Nicolai