[rspec-users] Testing with activerecord at ThoughtWorks (Stubbing vs real DB)

oren orengolan at gmail.com
Sat Jun 27 23:51:48 EDT 2009

I am reading the post by Fowler, 'Ruby at ThoughtWorks'.

He talks about testing with activerecord:

"Right at the beginning of our use of Ruby, there was a debate on how
best to organize testing in the presence of the Active Record database
layer in Rails. The basic problem is that most of the time,
performance of enterprise applications is dominated by database
access. We've found that by using a Test Double we can greatly speed
up our tests. Having fast tests is crucial to our test-intensive
development process. Kent Beck recommends a basic commit build of
under ten minutes. Most of our projects manage this these days, and
using a database double is a vital part of achieving it.

The problem with Active Record is that by combining database access
code with business logic, it's rather harder to create a database
double. The Mingle team's reaction to this was to accept that Rails
binds the database tightly and thus run all the commit tests against a
real database.

The contrary view was advocated most firmly by the Atlanta and Jersey
teams. Ruby has a powerful feature that allows you to redefine methods
at run-time. You can use this to take an active record class, and
redefine the the database access methods in that class as stubs. The
team started the gem unitrecord to help with this.

In the three years, we've not seen a generally accepted victor in this
debate. The Mingle team run a couple of thousand tests against a real
postgres database in around 8 minutes. (They parallelize the tests to
make use of multiple cores.) The Atlanta and Jersey teams consider it
valuable that their commit test runs in 2 minutes with stubs versus 8
minutes without. The trade-off is the simplicity of the direct
database tests versus the faster commit build of the stubbed tests.

While both teams are broadly happy with their positions in this
debate, the use of stubbing has led to another issue for the Atlanta/
Jersey teams. As the teams became familiar with using method stubbing,
they used it more and more - falling into the inevitable over-usage
where unit tests would stub out every method other than the one being
tested. The problem here, as often with using doubles, is brittle
tests. As you change the behavior of the application, you also have to
change lots of doubles that are mimicking the old behavior. This over-
usage has led both teams to move away from stubbed unit tests and to
use more rails-style functional tests with direct database access."

What do you think of the two tactics?
Also, What does it mean and where can I see examples of "running all
the commit tests against a real database" ?

Can I find it in "the rspec book" ?


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