When/why/should I unit test validations?

Rails
1

I run into this question each time I add a validation to my model.

Should I add a unit test for that validation?

On the one hand, I’ve heard/read the philosophy: “Q: What should I
test? A: Only the stuff you care about working”.

On the other hand I’ve heard/read, “You don’t need to test methods
provided by Rails – they are already tested by the test suite
included with the framework.”

If I put this in my model:

validates_uniqueness_of :name

Then I feel like I should write a unit test like
test_name_should_be_unique. But then that feels like I’m testing the
framework. If I’ve gone through the trouble of adding the validation
to my model, then it feels like I should go through the trouble of
testing the code I added to my model. Equivalently, if you’re in the
TDD/BDD driven camp, if I care about the behavior that the name should
be unique, I should write a test in which I try to add 2 records with
the same name field, verify the test fails, add the validation to my
model, and verify the test passes.

At this point, I start to think… DRY. Why should I write
substantially the same tests for every field in each model for which I
care that the field is unique (or present, or has a numericality,
etc…).

Are there test helper methods such as #test_uniqueness_of, or
#test_presence_of? I’ve never seen such functions, which makes me
think that they’re not important or useful enough for anybody (other
than myself) to have written and used. Since I have never had a good
idea that wasn’t replicated 100 times on the internet already, I tend
to think these sort of helper functions aren’t a good idea.

So I ask why not? What am I missing?

–wpd

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2

Patrick D. wrote:

I run into this question each time I add a validation to my model.

Should I add a unit test for that validation?

Yes.

On the one hand, I’ve heard/read the philosophy: “Q: What should I
test? A: Only the stuff you care about working”.

On the other hand I’ve heard/read, “You don’t need to test methods
provided by Rails – they are already tested by the test suite
included with the framework.”

Correct. But you do have to test that you are using those methods
correctly.

If I put this in my model:

validates_uniqueness_of :name

Then I feel like I should write a unit test like
test_name_should_be_unique. But then that feels like I’m testing the
framework.

No, you’re testing your use of the framework – after all, it would fail
if you forgot to add the validation, no matter how well tested Rails is!

(And you should really be using RSpec, not Test::Unit.)

If I’ve gone through the trouble of adding the validation
to my model, then it feels like I should go through the trouble of
testing the code I added to my model.

Right! You don’t have to test the framework code in detail, but you
should test that you at least put it into your model.

Equivalently, if you’re in the
TDD/BDD driven camp, if I care about the behavior that the name should
be unique, I should write a test in which I try to add 2 records with
the same name field, verify the test fails, add the validation to my
model, and verify the test passes.

Right! (I usually check valid? in circumstances like these.)

At this point, I start to think… DRY. Why should I write
substantially the same tests for every field in each model for which I
care that the field is unique (or present, or has a numericality,
etc…).

Are there test helper methods such as #test_uniqueness_of, or
#test_presence_of?

If there aren’t, you could write them.

I’ve never seen such functions, which makes me
think that they’re not important or useful enough for anybody (other
than myself) to have written and used. Since I have never had a good
idea that wasn’t replicated 100 times on the internet already, I tend
to think these sort of helper functions aren’t a good idea.

So you think that anything not already done is not worth doing? That
means you’ll never write any original code at all!

So I ask why not? What am I missing?

You’re missing the point of writing tests. :slight_smile:

Or you’re not missing anything except the fact that your instincts are
correct in this case. Absolutely, test that you have the right
validations in place.

–wpd

Best,

Marnen Laibow-Koser
http://www.marnen.org
[email protected]

3

You are right that everyone seems to disagree on this point. I think
validating the data is one of the most critical parts of an
application. I tend to validate at the db level and model level to
ensure integrity (as the app is not necessarily the only point of
entry to the db–psql prompt, another app, etc). If the application
cannot reliably trust the data it is likely to be buggy.

With that said, I like to write tests for the validations. This is
not because I don’t trust the tests done by rails, but because I don’t
trust myself. I could misspell (mispell?) one of the validations,
delete it accidently while I am refactoring, etc. With a few tests in
place, the upfront effort is repaid, because I can be confident it is
acting in the way I expect.

I haven’t used helpers like you ask, but I imagine they exist.

Just my 2 cents

Andrew

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4

Personally I like to test validations. I write my tests/specs first,
so
I write them for the validations that I think I should have.

Secondly because not all validations are as simple as
validates_presence_of :foo, there’s often other options, conditions or
blocks involved. Those
are often added as afterthoughts so you want to check they do whet you
expect. And don’t break
things.

I also like to check that the validation failure gives me the correct
message.

On Dec 25, 3:20 am, Andrew P. [email protected] wrote:

delete it accidently while I am refactoring, etc. With a few tests in
place, the upfront effort is repaid, because I can be confident it is
acting in the way I expect.

I haven’t used helpers like you ask, but I imagine they exist.

Just my 2 cents

Andrew

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