In many ways, testing software is like going out and getting exercise. You know you should do it, and you know it does you good, but it's also pretty easy to find an excuse to skip it (I'll make it up tomorrow).
So anything that makes testing easier is good, because it cuts down on the excuses not to do it.
One thing I've never really liked about the conventional xUnit-style testing frameworks was the setup and teardown structure. In these frameworks, a test case is a class, and setup and teardown are implemented by methods in that class. Each test is also a method, so the basic flow is
for each test method in the class
run setup
run the test method
run teardown
end
Nice and simple. Each test method got the benefit of a standard environment created by the setup method, and the teardown method got the job of tidying up after.
Except… when I'm writing tests, I typically want to set up lots of different scenarios. I'll want A and B and C, then A and B but not C, then A and not B, then A and D, and so on. I had two choices—write lots of test case classes, using subclassing to inherit common setup behavior, or write per-test method setup code (often factored out into helpers). In the end, I almost always did the latter, And that was tedious, and it made it harder to see the tests for the setup code.
I flirted with RSpec. Its spec framework seemed to have what I wanted. But I just couldn't get myself to enjoy using it. (I think it's a cat people/dog people kind of thing)
Enter shoulda
Then, a couple of weeks back, Mike Clark and Chad Fowler introduced me to shoulda. Shoulda isn't a testing framework. Instead, it extends Ruby's existing Test::Unit framework with the idea of test contexts. A context is a section of your test case where all the test methods have something in common. At it simplest, a context could be simply used as an annotation device (and, yes, this is a silly example):
context "My factorial method" do
should "return 1 when passed 0" do
assert_equal 1, fact(0)
end
should "return 1 when passed 1" do
assert_equal 1, fact(1)
end
should "return 6 when passed 3" do
assert_equal 6, fact(3)
end
end
The stuff in a context can share common setup code—just write a setup block.
class CartTest < Test::Unit::TestCase
context "An empty cart" do
setup do
@cart = orders(:wilmas_empty_cart)
end
should "have no line items" do
assert_equal 0, @cart.line_items.size
end
should "have a zero price" do
assert_equal 0, @cart.price
end
end
context "Some other context..." ...
end
end
So now, within a single test case I can set up multiple contexts, and each context can have its own environment.
But, take it back to my original problem. I often want to set up hierarchies of related environments for my tests. The shaoulda code handles this wonderfully, because it lets me nest contexts. For example, I'm adding a feature to our store that gives customers some additional information if, during checkout, their credit card transaction was initially rejected because the address was wrong, and was then accepted when they fixed the address. I wanted two tests, one without the prior address error, and one with.
To set up this environment, I needed to set up a shopping cart, create a dummy response from our payment gateway, and post that response to the application. In the case of the prior address error, I also wanted to inject an entry containing that error into the transactions associated with the order prior to generating the response.
With shoulda, I simply created some nested contexts. The top level context did the shared setup, and the inner contexts then set up appropriate environments for their tests. It looked like this:
context "Checking out" do
setup do
@cart = cart_named(:freds_full_cart)
@cart.prepare_for_store_authorize!
@params = approved_authnet_response(@cart)
end
context "with no AVS errors in CC transaction history" do
setup do
post :post_from_authnet_authorize, @params
end
should_redirect_to "{:action => :receipt}"
end
context "with AVS errors in CC transaction history" do
setup do
avs_error = CcTransaction.new(:response_code => 2, :response_reason_code => 27)
@cart.cc_transactions << avs_error
post :post_from_authnet_authorize, @params
end
should_redirect_to "{:action => :explain_avs_mismatch}"
end
end
The outer setup gets run before the execution of each of the inner contexts. And the setup in the inner contexts gets run when running that context. And shoulda keeps track of it all, so I get very natural error messages if an assertion fails. For example, if the test in the second context above fails, I'd get
Checking out with AVS errors in CC transaction history should
redirect to "{:action => :explain_avs_mixsmatch}".
So, now, I can finally set up my hierarchies of test environments in a natural way. It isn't revolutionary. It's just one less excuse for not testing…
