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RSpec matchers

Introduction

Reek offers matchers for RSpec you can easily include into your project.

There are 3 matchers available:

  • reek
  • reek_of
  • reek_only_of

Quickstart

Let's install the dependencies:

gem install reek
gem install rspec

And then use it like that in your spec file:

require 'reek'
require 'reek/spec'
require 'rspec'

RSpec.describe 'Reek Integration' do
  it 'works with Reek' do
    smelly_class = 'class C; def m; end; end'
    expect(smelly_class).not_to reek
  end
end

Running this via

rspec reek-integration-spec.rb

would give you:

Failures:

  1) Reek Integration works with Reek
     Failure/Error: expect(smelly_class).not_to reek
       Expected no smells, but got:
         C has no descriptive comment (IrresponsibleModule)
         C has the name 'C' (UncommunicativeModuleName)
         C#m has the name 'm' (UncommunicativeMethodName)
     # ./reek-integration-spec.rb:8:in `block (2 levels) in <top (required)>'

Finished in 0.00284 seconds (files took 0.28815 seconds to load)
1 example, 1 failure

Failed examples:

rspec ./reek-integration-spec.rb:6 # Reek Integration works with Reek

The matchers explained

reek

A very generic matcher that basically just tells you if something reeks, but not after what exactly. See the "Quickstart" example from above.

reek_of

Checks the target source code for instances of "smell type" and returns true only if it can find one of them that matches.

You can pass the smell type you want to check for as String or as Symbol:

  • :UtilityFunction
  • "UtilityFunction"

It is recommended to pass this as a symbol like :UtilityFunction. However we don't enforce this.

Additionally you can be more specific and pass in "smell_details" you want to check for as well e.g. "name" or "count" (see the examples below). The parameters you can check for are depending on the smell you are checking for. For instance "count" doesn't make sense everywhere whereas "name" does in most cases. If you pass in a parameter that doesn't exist (e.g. you make a typo like "namme") Reek will raise an ArgumentError to give you a hint that you passed something that doesn't make much sense.

So in a nutshell reek_of takes the following two arguments:

  • smell_type - The "smell type" we check for.
  • smells_details - A hash containing "smell warning" parameters

Examples

Without smell_details:

  reek_of(:FeatureEnvy)
  reek_of(:UtilityFunction)

With smell_details:

  reek_of(:UncommunicativeParameterName, name: 'x2')
  reek_of(:DataClump, count: 3)

Examples from a real spec

  expect(src).to reek_of(:DuplicateMethodCall, name: '@other.thing')

reek_only_of

See the documentation for reek_of.

Notable differences to reek_of:

  1. reek_of doesn't mind if there are other smells of a different type. "reek_only_of" will fail in that case.

  2. reek_only_of doesn't support the additional smell_details hash.