In the previous lesson, we established the utility of test-driven development (TDD) in maintaining your code and sanity. In this lesson, we’ll introduce you to your new best friend, the RSpec testing framework. It’s one of the most popular testing frameworks, having been downloaded more than 350 million times, at the time of this writing, and having been ported for use in Rails testing.
Look through these now and use them to guide your learning. By the end of this lesson, expect to:
At the most basic level, RSpec is a Domain Specific Language written in Ruby, or, for the rest of us, a language specialized for a particular task. In this case, the task is testing Ruby code. The
rspec gem comes packaged with all you need to get started, including five gems:
At this point, you may be wondering, Why RSpec? Surely, there are other frameworks out there, and you’d be right. There are. In fact, at one point, Ruby came bundled with Test::Unit and later Minitest as part of its standard library, the latter of which lives on in Rails. If you tend to be pessimistic (I’m sorry, I meant realistic), then the Wrong testing framework might be your cup of tea. Or perhaps you’re hungry and in the mood for something more substantial, in which case a side of Bacon might be what you need. At the end of the day, it doesn’t matter which framework you choose as long as you cultivate your testing skills. RSpec’s wider adoption, especially in the Rails community, is certainly reason enough to warrant familiarity with it, but implementing tests should be the end-all and be-all, rather than choosing a particular framework.
But enough proselytizing. Strap your helmet and buckle up; we’re going to jump right in.
Boot up your terminal and punch in
gem install rspec to install RSpec. Once that’s done, you can verify your version of RSpec with
rspec --version, which will output the current version of each of the packaged gems. Take a minute also to hit
rspec --help and look through the various options available.
cd into a project directory that you wish to configure for use with RSpec and type
rspec --init to initialize RSpec within the project. This will generate two files,
spec/spec_helper.rb, such that your project might look like:
project |__lib | |__script.rb | |__spec | |__spec_helper.rb | |__.spec
That’s it. Within two steps, you’re up and running with RSpec. That wasn’t so hard, was it?
How ‘bout a test to see the syntax? Let’s create a brand new “project” to get going. Create a new directory called “ruby_testing”, change into it, and initiate RSpec.
$ mkdir ruby_testing && cd ruby_testing
$ rspec --init
As expected, the output will read:
create .rspec create spec/spec_helper.rb
Run the tests from your terminal by using the
rspec command, which will return “No examples found.” That really shouldn’t surprise you, because we haven’t written any tests yet. If you’re still shocked… maybe take a short break, or come say hello to us in our Discord back-end channel.
No examples found. Finished in 0.00037 seconds (files took 0.21108 seconds to load) 0 examples, 0 failures
Let’s add our first test. Let’s say we want to create a calculator with a few methods that we want to test. True to TDD, we will write the tests prior to the code. The
spec/ folder is where all your tests will live. Using
touch on the command line or through your text editor, create
calculator_spec.rb within the
spec/ folder and add the following lines:
#spec/calculator_spec.rb RSpec.describe Calculator do describe "#add" do it "returns the sum of two numbers" do calculator = Calculator.new expect(calculator.add(5, 2)).to eql(7) end end end
Let’s go line by line.
describe is an RSpec keyword that defines an “Example Group”, or a collection of tests. It takes a class or a string as an argument and is passed a block (
describe blocks can be nested, such as on the second line of our test above. When describing a class, the following syntax is also valid:
#spec/calculator_spec.rb describe Calculator do #... end
it keyword defines an individual example (aka, test).
it takes a string argument and is also passed a block. This block is where our expectations of a method are expressed. In this particular case, when we pass 5 and 2 to the
#add method, we expect it to return 7. This is concisely expressed in our expectation clause, which uses one of RSpec’s equality matchers,
expect(calculator.add(5, 2)).to eql(7)
Simple, isn’t it? One more time, from the top:
describe the class
describe the method example group. Conventionally, the string argument for instance methods are written as “#method”, while string arguments for class methods are written as “.method”.
3. Write your test case/example with
4. Write your expectation using
expect method is also chained with
.to for positive expectations, or
.not_to for negative expectations. We prefer
.not_to. Also, limit one expect clause per test case.
Let’s move on. Run
rspec from the directory root, and watch the output.
An error occurred while loading ./spec/calculator_spec.rb. Failure/Error: describe Calculator do describe "#add" do it "returns the sum of two numbers" do calculator = Calculator.new expect(calculator.add(5, 2)).to eql(7) end end end NameError: uninitialized constant Calculator # ./spec/calculator_spec.rb:1:in `<top (required)>' No examples found. Finished in 0.0004 seconds (files took 0.16461 seconds to load) 0 examples, 0 failures, 1 error occurred outside of examples
So our first test returned an error. This is unsurprising.
NameError is essentially telling us that RSpec looked for a
Calculator class, but couldn’t find one. So let’s create it. From your project root, create a
lib/ folder, and inside,
calculator.rb with your class. We’ll also go ahead and begin the
#add method, otherwise RSpec will give us a similar error as the previous one when it looks for it:
#lib/calculator.rb class Calculator def add(a,b) end end
Finally, we must also tell the spec where the
Calculator class is being defined. This is easily done with
#spec/calculator_spec.rb require './lib/calculator' #=> add this describe Calculator do #... end
If you were to run ` rspec` this time, you’d get your first failure!
F Failures: 1) Calculator#add returns the sum of two numbers Failure/Error: expect(calculator.add(5, 2)).to eql(7) expected: 7 got: nil (compared using eql?) # ./spec/calculator_spec.rb:7:in `block (3 levels) in <top (required)>' Finished in 0.28565 seconds (files took 0.6273 seconds to load) 1 example, 1 failure Failed examples: rspec ./spec/calculator_spec.rb:5 # Calculator#add adds two numbers together
Our first failure is denoted by the
F at the top of the output. Congratulations! You’ve made it to the “red” portion of the “red-green-factor” cycle of TDD. RSpec provides a list of all the failures, with the expected vs. actual output of the method being tested. At the bottom of your output, RSpec also points to the line of the failing test, which in this case is where our
it block started.
Getting this method to “green” shouldn’t be too difficult. RSpec clearly provides a reason for the failure: it expected the output to be
7 when we provided the method with
(5, 2) as the parameters. Instead, it returned
nil. Why might that be? Well, our
#add does take two parameters…but it does nothing with them! Add the minimum amount of code necessary to get your test to pass:
#lib/calculator.rb class Calculator def add(a,b) a + b #=> add this end end
Then, run the test again to get a single dot, letting you know that your test has passed:
. Finished in 0.0032 seconds (files took 0.14864 seconds to load) 1 example, 0 failures
At this point, refactoring isn’t necessary. The
#add method is essentially a one line method. As you progress in your Ruby learning, however, you might find your methods getting more complex, and you might find that you have to make extra efforts to abide by SOLID principles. When that time comes, using RSpec and the “red-green-refactor” cycle will allow you to code with confidence, knowing that your classes and their behaviors continue to meet your specified expectations.
It’s time to put your newfound knowledge to good use. Let’s break our
#addmethod, written out for you below. Run the test to see the failure. Write the minimum code necessary to get both tests to pass, then refactor if necessary.
#spec/calculator_spec.rb describe Calculator do describe "#add" do it "returns the sum of two numbers" do # removed for brevity end # add this it "returns the sum of more than two numbers" do calculator = Calculator.new expect(calculator.add(2, 5, 7)).to eql(14) end end end
#divide) using a new
describeblock. Include at least one
itblock with an appropriate expectation clause. Get it to pass, and refactor if necessary.
rspec --format documentation. What’s different?
.rspec, one of the two files generated when RSpec is initialized in a project. If you liked the output you got with
--format documentation, you can use the
.rspecfile to hold that flag. In doing so, you won’t have to type it in every time you run your test suite. Open the file in your text editor and, on a new line, add
--format documentation. For more information on configuring RSpec, see the docs here.
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