estimating of testing effort as a percentage of development time [closed]

Question

Does anyone use a rule of thumb basis to estimate the effort required for testing as a percentage of the effort required for development? And if so what percentage do you use?

Answer 1

From my experience, 25% effort is spent on Analysis; 50% for Design, Development and Unit Test; remaining 25% for testing. Most projects will fit within a +/-10% variance of this rule of thumb depending on the nature of the project, knowledge of resources, quality of inputs & outputs, etc. One can add a project management overhead within these percentages or as an overhead on top within a 10-15% range.

Answer 2

The Google Testing Blog discussed this problem recently:

So a naive answer is that writing test carries a 10% tax. But, we pay taxes in order to get something in return.

(snip)

These benefits translate to real value today as well as tomorrow. I write tests, because the additional benefits I get more than offset the additional cost of 10%. Even if I don't include the long term benefits, the value I get from test today are well worth it. I am faster in developing code with test. How much, well that depends on the complexity of the code. The more complex the thing you are trying to build is (more ifs/loops/dependencies) the greater the benefit of tests are.