RSpec Basics

Introduction

The following is a basic introduction to some of the basic constructs in RSpec. This is by no means a complete guide, but should be enough to get started writing specs.

Table of contents

1. Specs and examples
2. Matchers

## 1. Specs and examples A set of tests for a given aspect of the code (class, module, method) is referred to as a **spec** and the individual tests are **examples**. The first step when writing a spec is to require the ``spec_helper`` file, and then create a ``describe`` block which defines what we're writing a spec for.

For example, to write a spec for the Group model, we would start like this:

  require 'spec_helper'

  describe Group do
  end

Describe blocks can be nested, so the next step would be to add a describe block for each method we wish to test. To keep things simple, we will just write a spec for the #pretty_category_name method:

  require 'spec_helper'

  describe Group do
    describe "#pretty_category_name" do
    end
  end

Now that things are organized, we can write some examples. To do this we write some it blocks for the different cases we wish to test. Since #pretty_category_name only has one line we will write an example describing how it should function:

  require 'spec_helper'

  describe Group do
    describe "#pretty_category_name" do
      it "should convert the suffix 'Group' of a class name to 'Project'"
    end
  end

When the method it is called this way, without a block, the example is considered pending. We can fill it in with some code to test the method.

  require 'spec_helper'

  describe Group do
    describe "#pretty_category_name" do
      it "should convert the suffix 'Group' of a class name to 'Project'" do
        group = SystemGroup.create!(:name => "sys_group")
        user  = User.create!(:login => "login", "password" => "password", ...)
        expect(group.pretty_category_name(user)).to eq("System Project")
      end
    end
  end

This is not ideal for a few different reasons:

• First, we are testing a class (SystemGroup) other than the one we are writing the spec for (Group).
• Second, the messy creation of the objects will become quite cumbersome if they have to be repeated for each example.
• Finally, the simple fact of having to define ALL attributes on a created object (e.g. because of the many validations on User) makes the code messy and draws focus away from what we are supposed be testing.

Let's deal with the issues one at a time. First, we can pull the object creation out of the example in two ways. The first is defining instance variables in a before(:each) block. A before(:each) block is simply some code run before each example in a given describe block, and can be used for set up:

  describe Group do
    before(:each) do
      @group = SystemGroup.create!(:name => "sys_group")
      @user  = User.create!(:login => "login", "password" => "password", ...)
    end

    describe "#pretty_category_name" do
      it "should convert the suffix 'Group' of a class name to 'Project'" do
        expect(@group.pretty_category_name(@user)).to eq("System Project")
      end
    end
  end

The other way is to use let statements. While before(:each) blocks can be used to run arbitrary code, let statements are specifically for setting up variables. In general, they are preferable, since they load lazily, i.e. the object isn't instantiated until the variable is used:

  describe Group do
    let(:group) { SystemGroup.create!(:name => "sys_group") }
    let(:user)  { User.create!(:login => "login", "password" => "password", ...) }

    describe "#pretty_category_name" do
      it "should convert the suffix 'Group' of a class name to 'Project'" do
        expect(group.pretty_category_name(user)).to eq("System Project")
      end
    end
  end

Note that the @ marker is no longer used. Now to avoid having to clutter our code with the definition of attributes we're not even testing, we can use factories. Factories allows us to create and save models with reasonable attributes. To use them, we define them in the file: "spec/factories/portal_factories.rb". We can add the factories we need in the following way:

  #################
  # User          #
  #################

  factory :user, class: NormalUser do
    sequence(:login)      { |n| "user#{n}" }
    sequence(:full_name)  { |n| "Bob #{n}" }
    sequence(:email)      { |n| "user#{n}@example.com" }
    password              "Password!"
    password_confirmation "Password!"
  end

  factory :normal_user, parent: :user, class: NormalUser do
    sequence(:login)      { |n| "normal_user_#{n}" }
  end

  #################
  # Group         #
  #################

  factory :group do
    sequence(:name) { |n| "group_#{n}" }
  end

And then, we can simplify our spec code as follows:

  describe Group do
    let(:group) { create(:group) }
    let(:user)  { create(:user) }

    describe "#pretty_category_name" do
      it "should convert the suffix 'Group' of a class name to 'Project'" do
        expect(group.pretty_category_name(user)).to eq("System Project")
      end
    end
  end

This creates the instance we need to run the code. Note that factories also have a build method to instantiate an object without saving it to the database. We have a problem now, however, in that the group is no longer a SystemGroup, and so will not produce the expected string. Furthermore, since the method is not meant to be used with the base Group class, we will get odd results. We could create another factory for a subclass of Group, but that would be overkill. All we need is one method: class. So instead of instantiating a whole new object, we can just stub the class method.

Stubbing is a testing technique whereby we intercept method calls on an object, either to block them or fix their return values. We can do so in the following way to stub the #class method:

  describe Group do
    let(:group) { create(:group) }
    let(:user)  { create(:user) }

    describe "#pretty_category_name" do
      it "should convert the suffix 'Group' of a class name to 'Project'" do
        allow(group).to receive(:class).and_return(SystemGroup)
        expect(group.pretty_category_name(user)).to eq("System Project")
      end
    end
  end

This idea of overkill is apparent as well in the case of the user object. It seems unnecessary to create an entire User object, just to pass it the method, and it is easier to use a mock object in this case. A mock object is a dummy object that simply takes the place of another object without doing anything. By default, it will not respond to any methods. Methods can be stubbed to add needed functionality. There are three methods we can use to create mock objects (See RSpec::ActiveModel::Mocks):

• double: create a basic mock object with no methods. A string is given as a first argument, this string is used to make error messages more readable. A hash can be given as second argument to conveniently define stubs.
• mock_model: create a mock ActiveRecord object. This mock will have a few basic ActiveRecord methods already stubbed out. Also, an optional argument can be given to define which model is being mocked (allowing the model to respond to #is_a? and #class).
• stub_model(model): create an instance of the actual ActiveRecord model, but with methods interacting with the db stubbed out.

For our purposes, we do not need any ActiveRecord functionality, so we can just use the standard double method.

  describe Group do
    let(:group) { create(:group) }
    let(:user)  { double("user") }

    describe "#pretty_category_name" do
      it "should convert the suffix 'Group' of a class name to 'Project'" do
        allow(group).to receive(:class).and_return(SystemGroup)
        expect(group.pretty_category_name(user)).to eq("System Project")
      end
    end
  end

By default, a mock object will only respond to methods that have been stubbed on it. If we find ourselves needing a mock object on which methods will be called, but without really being concerned about their return values, we can create a mock as a null object. A null object will respond to any methods stubbed on it with the return values defined, and will accept and ignore any other method calls without raising a MethodMissing exception. To convert a standard mock into a null object, we simply call the #as_null_object method on it:

  double("user").as_null_object

For the current example, however, this is unnecessary.

## 2. Matchers

One line that we did not discuss in the previous section was the line that actually defined our expectation:

  expect(group.pretty_category_name(user)).to eq("System Project")

RSpec has a very rich set of built in matchers to allow us to define our specs.

One simple way to produce a matcher is to use RSpec's be_xxx matchers. The xxx part of the method name should be a predicate method defined on the object being tested. For example:

  it "should not consider an empty object valid" do
    expect(Group.new).not_to be_valid
  end

The be_valid matcher will call the #valid? method on the user object to test the expectation. Another example would be:

  it "should start out with no users" do
    expect(create(:group).users).to be_empty
  end

This calls the #empty? method on the return value from the call to users.

There are also matchers for class comparisons. The be_a matcher uses #is_a? to compare classes:

  it "should be a Group" do
    expect(SystemGroup.new).to be_a(Group)
  end

The be_an_instance_of requires that the classes match exactly:

  it "should not be an instance of Group" do
    expect(SystemGroup.new).not_to be_an_instance_of(Group)
  end

We can also define expectations on method calls using the receive method. In the DataProvider class, we expect the #cache_prepare method to check that the cache is ready to be modified before creating directories. This expectation can be written as:

  it "should ensure that the cache is ready to be modified" do
    expect(SyncStatus).to receive(:ready_to_modify_cache)
    expect(provider.cache_prepare(userfile)).to be_truthy
  end

Note that the expectation is defined before the method is actually called. Also, not that a #receive call also effectively stubs out the method. This is by no means an exhaustive list of the types of matchers available in RSpec. For more documentation about all the matchers available see: https://relishapp.com/rspec/rspec-expectations/v/3-2/docs/built-in-matchers

For more information, consult the RSpec book or online documentation about RSpec 3.2.

Note: Original author of this document on RSpec is Tarek Sherif.