We've been introduced to the concepts of test driven development and reading and understanding RSpec tests before.
Every time you run learn to run a lab's tests, you are running an RSpec test suite - that's how we build labs on Learn.
You've been reading these tests for a while now, but TDD is a big topic and we're going to take a closer look at it here.
You're still not being asked to write your own tests. We're simply aiming to understand the purpose of tests, a bit on the philosophy behind them and a bit more on how to read RSpec tests better.
Remember, when we refer to RSpec or rspec, that is equivalent to running the learn or learn test command, which invokes the Learn test files in spec.
You must have the learn-co gem installed. If you set up your environment through Learn and have used the learn command before (very likely if you've made it this far), you are totally fine. Run learn now to confirm. If you're having trouble or aren't sure, ask a question on Learn!
RSpec is a testing tool for the Ruby programming language. Born under the banner of Behavior-Driven Development, it is designed to make Test-Driven Development a productive and enjoyable experience. The learn gem wraps rspec with additional functionality, so if you've been using learn, you've been using rspec.
Test Driven Development, or TDD, is a method for approaching a problem not through the implementation of the solution, but rather, through the expectations of a working solution. What that means is, instead of trying to write the code that solves the problem, you first define what the working code will do when it works, and then you write the implementation to make it work.
A classic programming problem is FizzBuzz. It is considered the Stairway to Heaven of programming because there are so many different ways to play it and everyone plays it.
The goal of FizzBuzz is to build a program that can take a number and if the number is evenly divisible by 3, it should return "Fizz", if it's divisible by 5, it should return "Buzz", and if it's divisible by both 3 and 5, it should return "FizzBuzz".
Let's approach solving this problem from a TDD approach. That means that we don't care about "how", but rather, we care about "what". What should the program do if it works correctly, not how it does it. We are going to write our expectations first, then our implementation.
Before we look at the RSpec syntax, let's just express our tests in plain English (also sometimes referred to as "pseudo-code").
Furthermore, we could also provide a negative case.
We don't care how that #fizzbuzz method works, nor how it's defined, we are just stating our expectations. And we're doing that first. When coding, it's important to have a target to shoot for; by writing your test first and stating your expectations of your code, you know your goal. You get to use your entire brain to think about just your goals, not how you'll get there, which adds clarity and focus to the problem.
The competent programmer is fully aware of the strictly limited size of his own skull; therefore he approaches the programming task in full humility.
— Edsger W. Dijkstra
Test-Driven Development allows us to fully utilize our mental capacity to clearly state the problem we're solving and then to 100% focus on implementing a solution. When you are just coding, you're actually focusing on stating the problem and the solution at the same time. You are thereby splitting your thinking in two, making you less effective at both.
It's the exact same reason you make a todo list. Also testing is not for present you, it's for future you.
— Joe M Burgess
RSpec is what's known as a DSL, or Domain Specific Language (also called a "Task Oriented Language" - a language designed for a specific kind of problem). It's a set of vocabulary (but actually just methods) that is useful for completing a specific kind of task. In this example, that task is describing our expectations and tests.
Here is an example of an RSpec test for one of the expectations above:
describe "fizzbuzz" do
it 'returns "Fizz" when the number is divisible by 3' do
fizz_3 = fizzbuzz(3)
expect(fizz_3).to eq("Fizz")
end
endSure, that code looks crazy and it's actually quite advanced, but we don't need to think about all of it, we just need to focus on 5 words: describe, it, expect, to, and eq. Let's break down that example.
describeThe first thing RSpec allows you to do with its DSL is to define what it is you are describing. As in, are we writing a test that describes how our Billing System works or are we writing a test that describes how #fizzbuzz works?
RSpec gives us the describe method. The argument we pass to the describe method is arbitrary; it doesn't really do anything besides document what exactly it is we're testing. Since we're writing a specification (a test) for #fizzbuzz, it makes sense to pass describe the string "fizzbuzz". describe also accepts a block, which will be covered shortly, but for now, just know that a block in Ruby starts with the do keyword. Every block that is opened must be closed. We use the end keyword to close the describe block.
The describe block can be thought of as a template for a spec (a test).
describe "The Thing We're Testing" do
# Specifications, that is, specific test examples, go here.
endA block is a simple unit of code that starts with the do keyword and ends with the end keyword. Blocks are a complex and wonderful part of the Ruby language and we don't need to focus on exactly what they are right now. It's best to think of a block just as a word used to describe a certain chunk, or unit, of code (almost like a paragraph). You can generally tell that something is a block because it is indented and grouped together. The aesthetics, the very form of the code, like in a poem, suggest a structure. That's a block.
Resources on Blocks:
itNow that we've created a structure to group our tests together using the describe method, we can move on to actually describing the desired functionality. Every specification in RSpec begins with the it method.
The it method, like the describe method, accepts an arbitrary string as an argument, namely, some text that says what we're currently interested in testing. Like all things in code, every it should be specifying one, only one, and exactly one, desired outcome or behavior.
Above we said that one functionality of #fizzbuzz is that it returns "Fizz" if the number is divisible by 3. So we can simply write that. It's totally up to you, the programmer, to decide the phrasing for your it specification, but a good starting point is a verb or action. it returns or it prints or it emails or it validates etc.
Also like the describe method, the it method accepts a block, beginning with the do keyword and ending with the end keyword, that will encapsulate, or group, the code that will test our expectation.
The it block template might look something like:
it 'returns "Fizz" when the number is divisible by 3' do
# Code that actually does what we're testing and confirms the desired result
endSo far, if we think of our RSpec test as a form of documentation, we can imagine it might read something like:
fizzbuzz
returns "Fizz" when the number is divisible by 3We're simply restating the problem and our expectations in the RSpec DSL. Now let's actually write the test for the specific example.
expect, to and eqOkay, let's refocus. Our goal is to test that when we call the #fizzbuzz method (which we are yet to build) and pass it the number 3, we expect it to equal "Fizz" if our code works correctly.
Outside of the context of our test suite, we could write an expression like:
fizzbuzz(3) == "Fizz"That is to say, when we evoke fizzbuzz(3), it should equal "Fizz". Taking advantage of the RSpec DSL, we can express that assertion as follows:
# First, get the return value from fizzbuzz(3), store it in a variable, fizz_3
fizz_3 = fizzbuzz(3)
# Next, our expectation that the value of fizz_3 should be "Fizz"
expect(fizz_3).to eq("Fizz")So three new RSpec methods, expect, to, and eq.
expect() is a method that accepts our unknown value or variable, the thing we're testing. So for instance, in a simple math equation, imagine the following:
x = 1 + 1
expect(x)Since x is the unknown variable, we'd be testing the expectation of the value of x, so we pass that value to the expect method. I can imagine it's weird to think of the variable x as an unknown value worth confirming. You're thinking, "It's obviously 2!" But the truth is, you're making the assumption that Ruby has a correct notion of arithmetic. As our programs become more complex and we use more variables, it's very important to constantly validate our assumptions with expectations and testing. Let's finish the example.
In addition to the expect(x) call, we need to communicate what we expect x to be equal to. To accomplish this, we chain a to() method to the expect(), so it simply looks like:
x = 1 + 1
expect(x).toThen finally we use what is known as a matcher, eq, to specify our expectation: that we expect the value of x, passed to the expect method, to equal (to eq) 2.
x = 1 + 1
expect(x).to eq(2)You won't have to write your own tests for a while, so don't worry about mastering the expect, to, and eq usage. The important part is that you can read the DSL and understand what it is trying to suggest.
First, fork and clone this lab and open it on your machine. Read the remainder of this tutorial and follow along by executing certain commands and writing certain code in this lab on your computer.
So the entire FizzBuzz test looks like this:
File: spec/fizzbuzz_spec.rb
require_relative './spec_helper.rb'
describe "fizzbuzz" do
it 'returns "Fizz" when the number is divisible by 3' do
fizz_3 = fizzbuzz(3)
expect(fizz_3).to eq("Fizz")
end
it 'returns "Buzz" when the number is divisible by 5' do
fizz_5 = fizzbuzz(5)
expect(fizz_5).to eq("Buzz")
end
it 'returns "FizzBuzz" when the number is divisible by 3 and 5' do
fizz_15 = fizzbuzz(15)
expect(fizz_15).to eq("FizzBuzz")
end
it 'returns nil when the number is not divisible by 3 or 5' do
fizz_4 = fizzbuzz(4)
expect(fizz_4).to eq(nil)
end
endRemember, your goal here is not to be able to write that test suite, yet. Your goal, rather, is to understand what that test suite is describing about your code, about your solution. When I read that, I think the following things:
#fizzbuzz that accepts one argument.rspec via learnNow, from within the directory of this file, type the learn command. Your terminal should have an output that looks something like this:
fizzbuzz
returns "Fizz" when the number is divisible by 3 (FAILED - 1)
returns "Buzz" when the number is divisible by 5 (FAILED - 2)
returns "FizzBuzz" when the number is divisible by 3 and 5 (FAILED - 3)
returns nil when the number is not divisible by 3 or 5 (FAILED - 4)
Failures:
1) fizzbuzz returns "Fizz" when the number is divisible by 3
Failure/Error: fizz_3 = fizzbuzz(3)
NoMethodError:
undefined method `fizzbuzz' for #<RSpec::ExampleGroups::Fizzbuzz:0x007f994ac67600>
# ./spec/fizzbuzz_spec.rb:5:in `block (2 levels) in <top (required)>'
2) fizzbuzz returns "Buzz" when the number is divisible by 5
Failure/Error: fizz_5 = fizzbuzz(5)
NoMethodError:
undefined method `fizzbuzz' for #<RSpec::ExampleGroups::Fizzbuzz:0x007f994ac65940>
# ./spec/fizzbuzz_spec.rb:10:in `block (2 levels) in <top (required)>'
3) fizzbuzz returns "FizzBuzz" when the number is divisible by 3 and 5
Failure/Error: fizz_15 = fizzbuzz(15)
NoMethodError:
undefined method `fizzbuzz' for #<RSpec::ExampleGroups::Fizzbuzz:0x007f994ac64310>
# ./spec/fizzbuzz_spec.rb:15:in `block (2 levels) in <top (required)>'
4) fizzbuzz returns nil when the number is not divisible by 3 or 5
Failure/Error: fizz_4 = fizzbuzz(4)
NoMethodError:
undefined method `fizzbuzz' for #<RSpec::ExampleGroups::Fizzbuzz:0x007f994ac5ed20>
# ./spec/fizzbuzz_spec.rb:20:in `block (2 levels) in <top (required)>'
Finished in 0.00236 seconds (files took 0.39876 seconds to load)
4 examples, 4 failures
Failed examples:
rspec ./spec/fizzbuzz_spec.rb:4 # fizzbuzz returns "Fizz" when the number is divisible by 3
rspec ./spec/fizzbuzz_spec.rb:9 # fizzbuzz returns "Buzz" when the number is divisible by 5
rspec ./spec/fizzbuzz_spec.rb:14 # fizzbuzz returns "FizzBuzz" when the number is divisible by 3 and 5
rspec ./spec/fizzbuzz_spec.rb:19 # fizzbuzz returns nil when the number is not divisible by 3 or 5When we installed the RSpec and Learn.co gems, we got the learn command. When you type learn and press enter, you are running your test suite — not your program. We haven't even written our FizzBuzz program yet.
So how does that work?
When we run the learn command, in a nutshell, here is what happens:
spec for all files that end with the pattern _spec.rb. Why the spec folder and the _spec.rb pattern? No reason, just convention._spec.rb file.In the spec directory for this lab, there are 2 files: spec_helper.rb, which does not match the pattern of ending with a _spec.rb, and fizzbuzz_spec.rb, which does. So RSpec will open the second file and have Ruby execute it.
If you look at spec/fizzbuzz_spec.rb, there's only 1 line of it that we haven't covered: require_relative './spec_helper.rb'. All this line does is tell Ruby to load the contents of the neighboring file, specified by the starting . (meaning the current directory), and the file name: spec_helper.rb. If you look within spec_helper.rb, you'll see that it's basically configuring how RSpec should run and at this point is totally unimportant. One thing to note, though, is if we need to have our actual test file load any other file, that require_relative line becomes even more interesting.
Again, the learn command wraps RSpec and provides some default options (namely, --format documentation, which controls how your test results print), and, though you will see approximately the same output with rspec or learn, we recommend using learn.
Let's look at the output RSpec gives us (just run learn again), and dig into it a bit.
rspec
Run options: include {:focus=>true}
All examples were filtered out; ignoring {:focus=>true}
fizzbuzz
returns "Fizz" when the number is divisible by 3 (FAILED - 1)
returns "Buzz" when the number is divisible by 5 (FAILED - 2)
returns "FizzBuzz" when the number is divisible by 3 and 5 (FAILED - 3)
returns nil when the number is not divisible by 3 or 5 (FAILED - 4)The first two lines of output are descriptive; RSpec is simply telling us what it did.
The lines that follow are important, each line represents a failure. As the test suite runs, RSpec will spit out red text line for every failed expectation (every it block). RSpec will also spit out lines with green text for every passing test.
Right now, the entire test suite is failing, which makes sense. We haven't written any code! That's an important point, and I think Steve Klabnik said it best:
Programming is a movement from a broken state to a working state. That means you spend the majority of your time with things being broken. Hell, if it worked, you'd be done programming.
If you're new to programming, you're probably used to things working. So when they are broken, it's scary. In programming, you have to feel the exact opposite way. It is totally normal for everything to be broken. As you code, you fix things, one by one, and then, when it all works, you're done for the day.
So, sure, we know philosophically that the reason why our tests are failing is because we did nothing to make them pass. But what, specifically, is the reason they are failing?
Our rspec output continues with a summary of each individual failure:
Failures:
1) fizzbuzz returns "Fizz" when the number is divisible by 3
Failure/Error: fizz_3 = fizzbuzz(3)
NoMethodError:
undefined method `fizzbuzz' for #<RSpec::Core::ExampleGroup::Nested_1:0x007fbdd2230428>
# ./spec/fizzbuzz_spec.rb:5:in `block (2 levels) in <top (required)>'In the failure output, the first line fizzbuzz returns "Fizz" when the number is divisible by 3 tells us the description of the test. The second line Failure/Error: fizz_3 = fizzbuzz(3) tells us the line that caused the failure or error. In this case, it is an error, and we see the Ruby error.
NoMethodError:
undefined method `fizzbuzz' for #<RSpec::Core::ExampleGroup::Nested_1:0x007fbdd2230428>
# ./spec/fizzbuzz_spec.rb:5:in `block (2 levels) in <top (required)>'We have a NoMethodError. There is no method #fizzbuzz, and the line that is important is line 5 of /spec/fizzbuzz_spec.rb. The rest of it is just RSpec noise (the thing about RSpec::Core::ExampleGroup::Nested_1 is pretty meta and not worth going into here).
So, why did our test fail? Because we did not define a #fizzbuzz method.
It is finally time to actually program a solution to FizzBuzz. The first question to answer is where to put our solution, the actual code we care about, the program we're writing. Let's look at our current directory structure:
rspec-fizzbuzz/
.bundle/
config
spec/
fizzbuzz_spec.rb
spec_helper.rb
.learn
.rspec
CONTRIBUTING.md
fizzbuzz.rb
Gemfile
Gemfile.lock
LICENSE.md
README.md The spec directory is for our tests. There's a more advanced folder structure to separate the different kinds of tests you might encounter: unit, acceptance, etc. For now, while our scripts are simple, we'll typically have one _spec.rb test for each lab.
We're not going to put the heart of our application in the spec folder — that wouldn't make sense. We want to keep our code organized so developers can easily guess the context or part of the system a file corresponds to. It's a measure of symmetry to our code for tests to go in the spec directory.
In a larger program, I would put my code in a lib directory. In this example, fizzbuzz.rb is in the root directory, right alongside this README.md.
fizzbuzz.rb is where we're going to code the core of our program: a simple method, #fizzbuzz, that, when invoked by the tests above, will behave as we specified. For now though, let's just fix the first rspec failure.
The first failure is that there is no method known as #fizzbuzz. Let's simply define that method.
File: fizzbuzz.rb
def fizzbuzz
endNow, when we run learn, we should expect to see a new sort of error.
Run: learn
1) fizzbuzz returns "Fizz" when the number is divisible by 3
Failure/Error: fizz_3 = fizzbuzz(3)
NoMethodError:
undefined method `fizzbuzz' for #<RSpec::Core::ExampleGroup::Nested_1:0x007fd2f21083b8>
# ./spec/fizzbuzz_spec.rb:5:in `block (2 levels) in <top (required)>'Don't panic! It's the same exact failure, our old friend NoMethodError, as though we never defined #fizzbuzz. But look, after all this, we finally did some work and added a clearly defined #fizzbuzz method to fizzbuzz.rb. So why is the test still complaining?
Let's try loading a Ruby environment from within our project directory and playing with the #fizzbuzz method ourselves for a second.
From within the project directory (the name will start with rspec-fizzbuzz-, followed by a code indicating your cohort or curriculum track), fire up irb, the Interactive Ruby Shell, a real-time Ruby prompt for executing arbitrary code. For instance:
// ♥ irb
2.2.3 :001 > 1+1
=> 2From within your new IRB shell, try calling the #fizzbuzz method that's defined in fizzbuzz.rb:
// ♥ irb
2.2.3 :001 > fizzbuzz
NameError: undefined local variable or method `fizzbuzz' for main:Object
from (irb):1
from /Users/avi/.rvm/rubies/ruby-2.2.3/bin/irb:11:in `<main>'There's our error. We tried calling #fizzbuzz and IRB complains that it doesn't know what we're talking about. Why? Well, when did we tell IRB to actually load the contents of fizzbuzz.rb? We didn't. Similarly, nowhere in our test runtime did we tell RSpec to actually load the contents of, read, or require fizzbuzz.rb. Try this in IRB:
// ♥ irb
2.2.3 :001 > require './fizzbuzz.rb'
=> true
2.2.3 :002 > fizzbuzz
=> nilAs you can see, by requiring the fizzbuzz.rb file, we were able to call the #fizzbuzz method.
Let's add that requirement to our RSpec test suite, so that our tests know to load the code they're supposed to be testing.
Edit: spec/fizzbuzz_spec.rb
require_relative './spec_helper.rb'
require_relative '../fizzbuzz.rb'Now we're telling fizzbuzz_spec.rb to load both spec_helper.rb and fizzbuzz.rb.
Run the test suite one more time with learn. You should see failures in line with the following:
1) fizzbuzz returns "Fizz" when the number is divisible by 3
Failure/Error: fizz_3 = fizzbuzz(3)
ArgumentError:
wrong number of arguments (1 for 0)
# ./fizzbuzz.rb:1:in `fizzbuzz'
# ./spec/fizzbuzz_spec.rb:6:in `block (2 levels) in <top (required)>'Read that error message; it's brand new! Getting a new error message is a sign of progress. It's one more hint the computer is giving you, one more clue to drive your investigation forward. Now it's complaining that our tests are calling the #fizzbuzz method with an argument; however, our definition of #fizzbuzz accepts no arguments. You'll fix that next, but it's important to realize our test suite is now wired up correctly. We can continue building out our #fizzbuzz method and running our specs against that code until we have it working.
That's the end of the tutorial part of this lab. You know enough about RSpec and Ruby to continue solving this in a test-driven manner. As you define your #fizzbuzz method, remember that you can always play with it in IRB. For instance, load an IRB terminal and try (line by line):
def fizzbuzz(int)
if int % 3 == 0 # if the number int is divisible by 3
"Fizz" # Go fizz
end
end
fizzbuzz(3) # => You should see a return of "Fizz"
fizzbuzz(5) # => You should see a return of nil
fizzbuzz() # => You should get an ArgumentErrorHelpful Tip: You can try out code in IRB and then copy it to your program files as you get it working. You can also use Pry, an IRB alternative, by placing the line require 'pry' at the top of fizzbuzz.rb and placing binding.pry inside the method before running RSpec.
Good luck!