- Build methods that utilize flow control
- Read and understand test output to develop a working program
- Gain more familiarity with the concept of test driven development
We've been introduced to the concept 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 a Learn test file in spec and running the learn or learn test command.
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 what 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").
- We expect fizzbuzz(3) to return "Fizz"
- We expect fizzbuzz(5) to return "Buzz"
- We expect fizzbuzz(15) to return "FizzBuzz"
Furthermore, we could also provide a negative case.
- We expect fizzbuzz(4) to return nil or nothing or ""
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.
The 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:
- Why's Guide to Blocks
- Understanding Ruby Blocks, Procs, and Lamdbas
- Codecademy on Blocks
- RubyMonk on Blocks
Now that we've created a structure to group our tests together using the describe method, we can move onto 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 3
We're simply restating the problem and our expectations in the RSpec DSL. Now let's actually write the test for the specific example.
Okay, 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. We do this in a weird way, 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 result of our expectation, 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 is located in spec/fizzbuzz_spec.rb:
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:
- I need a method called
fizzbuzzthat accepts one argument. - When I call that method and pass it a number divisible by 3, like the number 3 for instance, that method should return the string "Fizz".
- When I call that method and pass it a number divisible by 5, like the number 5 for instance, that method should return the string "Buzz".
- When I call that method and pass it a number divisible by 3 and 5, like the number 15 for instance, that method should return the string "FizzBuzz".
- When I call that method and pass it a number not divisible by 3 or 5, like the number 4 for instance, that method should return nil.
Now, from within the directory of this file, type the learn command. Your terminal should have an output that looks something like this:
fizzbuzz
returns "Buzz" when the number is divisible by 5 (FAILED - 1)
returns "FizzBuzz" when the number is divisible by 3 and 5 (FAILED - 2)
returns nil when the number is not divisible by 3 or 5 (FAILED - 3)
returns "Fizz" when the number is divisible by 3 (FAILED - 4)
Failures:
1) fizzbuzz returns "Buzz" when the number is divisible by 5
Failure/Error: fizz_5 = fizzbuzz(5)
NoMethodError:
undefined method `fizzbuzz' for #<RSpec::ExampleGroups::Fizzbuzz:0x007fb0645b1f00>
# ./spec/fizzbuzz_spec.rb:10:in `block (2 levels) in <top (required)>'
2) 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:0x007fb0645b1168>
# ./spec/fizzbuzz_spec.rb:15:in `block (2 levels) in <top (required)>'
3) 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:0x007fb0645b03f8>
# ./spec/fizzbuzz_spec.rb:20:in `block (2 levels) in <top (required)>'
4) fizzbuzz returns "Fizz" when the number is divisible by 3
Failure/Error: fizz_3 = fizzbuzz(3)
NoMethodError:
undefined method `fizzbuzz' for #<RSpec::ExampleGroups::Fizzbuzz:0x007fb0645ab650>
# ./spec/fizzbuzz_spec.rb:5:in `block (2 levels) in <top (required)>'
Finished in 0.00121 seconds (files took 0.23681 seconds to load)
4 examples, 4 failures
Failed examples:
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 5
rspec ./spec/fizzbuzz_spec.rb:4 # fizzbuzz returns "Fizz" when the number is divisible by 3
When we installed the RSpec and Learn.co gem, we got the learn command. When you run the learn command, you are running your test suite — not your program. We haven't even written our fizzbuzz program yet.
So how does that work?
Well, when you type in learn, in a nutshell, here is what happens.
- RSpec looks in a directory named
specfor all files that end with the pattern_spec.rb. Why thespecfolder and the_spec.rbpattern? No reason, just convention. - For each of those files, it executes the Ruby code within those files.
- During that execution, RSpec pays attention to the results of each test and prints out a nice summary of what happened (which is the output above that we're going to dissect in a minute).
Within the spec directory there are 2 files, spec_helper.rb, which does not match the pattern of ending with a _spec.rb, and then a file called fizzbuzz_spec.rb which does match that pattern. So RSpec will open that 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: the first — 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 you will see the same output with rspec or learn, we recommend using learn.
Let's look at the output RSpec gave us and dig into it a bit.
rspec
Run options: include {:focus=>true}
All examples were filtered out; ignoring {:focus=>true}
FFFF
The first two lines of output are descriptive, RSpec is simply telling us what we did.
The line with FFFF is important. F stands for a failure. As the test suite runs, RSpec will spit out an F for every failed expectation (every it block). RSpec will spit out a . 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 do we put our solution, the actual code we care about, the program we're writing. Let's look at our current directory structure.
rspec-fizzbuz/
spec/
fizzbuzz_spec.rb
spec_helper.rb
.learn
.rspec
fizzbuzz.rb
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 basically write one spec for each lab.
We're not going to put the heart of our application in the spec folder, that doesn'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 tests 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.
fizzbuzz.rb is where we're going to code the core of our program––a simple method, fizzbuzz that when evoked in the tests above, will behave as we specified. For now though, let's just fix our first error.
The error we were dealing with is that there is no method known as fizzbuzz. Let's simply define that method.
File: fizzbuzz.rb
def fizzbuzz
endNow, when we run our spec suite, we could expect to see a new sort of error. After all, we finally started solving fizzbuzz by at least defining a method to solve fizzbuzz.
Run: rspec
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 error, our old friend, NoMethodError, as though we never defined fizzbuzz. But look, after all this, we finally did some work and created the fizzbuzz.rb with a clearly defined fizzbuzz method and our tests are still complaining that we didn't define that method. Why?
Let's try this, let's load a Ruby environment from within our project directory and just play with the fizzbuzz method ourselves for a second.
From within rspec-fizzbuzz fire up irb, the Interactive Ruby Shell, a REPL, or real time ruby prompt for executing arbitrary ruby. For instance (remember $ means that command, irb was entered into your bash prompt:
$ irb
2.0.0-p247 :001 > 1+1
=> 2
2.0.0-p247 :002 >
From within your new IRB shell, try calling the fizzbuzz method that's defined in fizzbuzz.rb:
2.0.0-p247 :001 > fizzbuzz
NameError: undefined local variable or method `fizzbuzz' for main:Object
from (irb):1
from /Users/avi/.rvm/rubies/ruby-2.0.0-p247/bin/irb:16: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 our fizzbuzz.rb? We didn't. And no where in our test runtime did we tell our tests to actually load the contents, to read, to require, fizzbuzz.rb. Try this in IRB
2.0.0-p247 :001 > fizzbuzz
NameError: undefined local variable or method `fizzbuzz' for main:Object
from (irb):1
from /Users/avi/.rvm/rubies/ruby-2.0.0-p247/bin/irb:16:in `<main>'
2.0.0-p247 :001 > require './fizzbuzz.rb'
=> true
2.0.0-p247 :001 > fizzbuzz
=> nil
As you can see, by requiring the fizzbuzz.rb file, we were able to call the fizzbuzz method.
Let's add that requirement, the loading of our actual program, to our test, so that when our tests run, they can rely on our program.
Edit: spec/fizzbuzz_spec.rb
require_relative './spec_helper.rb'
require_relative '../fizzbuzz.rb'Now we're telling our fizzbuzz_spec to load both spec_helper.rb and fizzbuzz.rb.
Run the test suite one more time with rspec, you should see failures in line with:
1) fizzbuzz returns nil when the number is not divisible by 3 or 5
Failure/Error: fizz_4 = fizzbuzz(4)
ArgumentError:
wrong number of arguments (1 for 0)
# ./fizzbuzz.rb:1:in `fizzbuzz'
# ./spec/fizzbuzz_spec.rb:21: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, but it's important to realize our test suite is now all wired up and 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 have enough about RSpec and Ruby to continue solving this in a test driven manner. As you define your fizzbuzz method, remember, 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 argument errorHelpful Tip: You can try code in IRB and then copy it to your program files as you get it working. You can also use Pry by placing the line require 'pry' at the top of your fizzbuzz.rb and placing binding.pry inside the method before running RSpec.
Good luck!