# Preloading data before running tests?

**URL:** <https://www.ruby-forum.com/t/preloading-data-before-running-tests/190048>\
**Category:** Rails\
**Created:** [June 12, 2010, 12:27am UTC](https://www.ruby-forum.com/t/preloading-data-before-running-tests/190048 "2010-06-12T00:27:33Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![fearless\_fool](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/5e9695/32.png) [@fearless\_fool](https://www.ruby-forum.com/u/fearless_fool)\
**Post date:** [June 12, 2010, 12:27am UTC](https://www.ruby-forum.com/t/preloading-data-before-running-tests/190048/1 "2010-06-12T00:27:33Z")

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Okay - I’m stumped: is there a way to run unit tests without blowing  
away data preloaded into the test database?

Details: our system uses a TimeDimension table – think of it as a  
datetime that’s been highly decorated with additional info, such as  
whether or not it’s a holiday and other dimensional database goodness.  
Many of our unit tests depend on the presence of the TimeDimension  
table, but with ~21K rows it’s too expensive to recompute before every  
test.

I _thought_ that seeds.rb could be used to pre-populate the db before  
running unit tests, but I traced through “rake test:units” and it  
appears to blow away existing data before running the tests.

For example, the following does NOT work:

bash$ export RAILS\_ENV=test # work with test db  
bash$ rake db:reset # drop, recreate, seed test db  
bash$ rake test:units # blows away the seeds before running (ugh)

So: Is there a way to load persistent data into tables that won’t get  
nuked running unit tests? (To make it perfectly clear: rollbacks after  
each test are fine, its just the initial clearing of the database that I  
want to avoid.)

Ideas? Am I missing some obvious rake command or option?

- ff

btw:

bash$ rails --version ; rake --version ; ruby --version  
Rails 2.3.8  
rake, version 0.8.7  
ruby 1.9.1p376 (2009-12-07 revision 26041) [powerpc-darwin9.8.0]

---

<div class="post-metadata">

**Author:** ![fearless\_fool](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/f/5e9695/32.png) [@fearless\_fool](https://www.ruby-forum.com/u/fearless_fool)\
**Post date:** [June 15, 2010, 9:49pm UTC](https://www.ruby-forum.com/t/preloading-data-before-running-tests/190048/2 "2010-06-15T21:49:00Z")

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Fearless F. wrote:

> Okay - I’m stumped: is there a way to run unit tests without blowing  
> away data preloaded into the test database?
> 
> Details: our system uses a TimeDimension table – think of it as a  
> datetime that’s been highly decorated with additional info, such as  
> whether or not it’s a holiday and other dimensional database goodness.  
> Many of our unit tests depend on the presence of the TimeDimension  
> table, but with ~21K rows it’s too expensive to recompute before every  
> test.
> 
> I _thought_ that seeds.rb could be used to pre-populate the db before  
> running unit tests, but I traced through “rake test:units” and it  
> appears to blow away existing data before running the tests.
> 
> For example, the following does NOT work:
> 
> bash$ export RAILS\_ENV=test # work with test db  
> bash$ rake db:reset # drop, recreate, seed test db  
> bash$ rake test:units # blows away the seeds before running (ugh)

Yes, that’s expected and proper behavior. Unit tests that depend on  
pre-existing conditions/data are fragile. They are called “Unit Tests”  
because they are intended to create isolated examples that are not  
subject to any pre-existing conditions, such as pre-existing data. Unit  
tests should set up all conditions needed to satisfy the examples  
defined in the current test, and then “tear down” said conditions before  
executing subsequent tests.

> So: Is there a way to load persistent data into tables that won’t get  
> nuked running unit tests? (To make it perfectly clear: rollbacks after  
> each test are fine, its just the initial clearing of the database that I  
> want to avoid.)

Not unless you hack your test environment to do, but you do this at your  
own risk. By doing so you are violating a core principal of Unit  
Testing.

> Ideas? Am I missing some obvious rake command or option?

My recommendation is to study up on proper testing techniques. You say  
you have 20K+ rows in one of your production/development tables. Are you  
going to create 20K+ tests to provide examples for every one of those  
pre-conditions? If not they you don’t need 20K+ rows in your test  
database table. You probably only need two or three good examples of  
that data to satisfy the examples you’ll be writing.

Besides that, if the data you mentioned is only needed to satisfy a  
dependency for test not directly related to that data, then you can  
provide your unit tests with objects from a testing data factory such as  
Machinist or Factory Girl.

> **[GitHub - notahat/machinist: Fixtures aren't fun. Machinist is.](https://github.com/notahat/machinist)**
>
> Fixtures aren't fun. Machinist is. Contribute to notahat/machinist development by creating an account on GitHub.

> **[GitHub - thoughtbot/factory\_bot: A library for setting up Ruby objects as...](https://github.com/thoughtbot/factory_bot)**
>
> A library for setting up Ruby objects as test data. - GitHub - thoughtbot/factory\_bot: A library for setting up Ruby objects as test data.