Being able to run tests that we would not have had time to run manually is one of the benefits of automated testing; we should be able to measure this benefit in some way.
What is EMTE?
EMTE stands for "Equivalent Manual Test Effort" and is a way of measuring the benefit of running automated tests.
If an automated test (A) would have taken 4 hours to run manually, then its EMTE is 4 hours; another test (B) that would have taken 7.5 hours to run manually has an EMTE of 7.5 hrs.
In a test cycle, if Test A is run five times, and Test B is run twice, then the EMTE for that cycle is 5*4 hrs + 2*7.5 hrs = 20 + 15 = 35 hours EMTE.
What is EMTE used for?
EMTE can be used as a way to measure a benefit of test automation (automated running of functional tests).
When tests are automated, they can be run in much less time than they could be run manually. Our tests A and B may be able to run in 5 and 10 minutes respectively, for example. So we can achieve "4 hours' worth" of manual testing in 5 minutes of automated testing. Whenever we run Test A, we can "clock up" 4 hours of EMTE.
Is EMTE a good thing?
Yes, because it is a way to show the benefit of automation.
Costs (of automation as well as other things) tend to become visible by themselves - managers see that people are spending time on the automation. But what is the benefit of this automation? If you don't make benefits visible to managers, there is a risk that they will not see the benefits, and may eventually conclude that there are no benefits. EMTE is one way to make an automation benefit visible.
So how could it be a bad thing?
I have had discussions with a couple of people recently (thanks Julian and Wade) about abusing EMTE, and yes, it can be abused (as any metric can). Here is how it could be mis-used:
"Test A takes 5 minutes, so let's run it 12 times every hour for 2 hours. This gives 24*4 hours of EMTE = 96 hours. This will make us look really great!"
The problem is that after the first run, the other 23 runs are being done just for the sake of looking good, not for a valuable benefit in terms of running that test. This is an abuse of EMTE, and is a bad thing.
What to do about it?
Use EMTE (and other measures of the benefit of test automation) sensibly.
Perhaps only "count" EMTE once a day, however many times a test is run? (e.g. in continuous integration testing)
In what other ways can the benefit of automation be shown? (e.g. more coverage, freeing testers to find more bugs, number of times tests are run, more variety of data used?)
Have you encountered the abuse of this (or other automation) measures? How have you solved the problem? (Please comment, thanks!)