[rspec-users] BDD and Performance

Matt Wynne matt at mattwynne.net
Wed Dec 29 05:18:21 EST 2010

On 29 Dec 2010, at 05:49, Shea Levy wrote:

> Hi all,
> What's the best way to implement performance enhancements from the outside-in? For example, if I'm working test-free and I know I'm going to be looking up my Shops by phone number often, I'll write a migration to make phone_number an index of the shops table. What feature(s) and spec(s) would I write to drive me to that migration?
> Cheers,
> Shea Levy

I try to think of an example, from the user's perspective, that describes a goal I'm trying to meet.

So in the case of the shop, I might say:

    Given there are 10,000 Shops in the system
    When I look up a Shop by it's phone number
    Then I should see the result within 0.2 seconds

Just as with business rules, forcing yourself to describe the goal in such concrete terms can trigger some very interesting and useful conversations.

Obviously you will find that these kinds of tests behave much less deterministically than business rule tests, so it's useful if you can make your development and test environments as homogenous as possible. You can also help smooth this out by making the scenario work with averages instead:

    Given there are 10,000 Shops in the system
    When I perform 100 searches for a Shop by phone number
    Then on average, I should see the result within 0.2 seconds

These sorts of tests are also much slower than business rule tests, because they tend to need lots of data and to take several samples to get their average. It's worth tagging them to exclude them from your check-in build run and running them in a nightly build instead.

Hope that helps.


matt at mattwynne.net
07974 430184

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