Class: RuboCop::Cop::Vicenzo::RSpec::TopLevelLet

Inherits:
RSpec::Base
  • Object
show all
Includes:
TopLevelDefinition
Defined in:
lib/rubocop/cop/vicenzo/rspec/top_level_let.rb

Overview

A let declared straight inside the top-level example group is the root of the nested redefinition problem. Declare it in the group whose examples read it.

The top-level group is the widest scope a file has: a let born there is handed to every example, including all the ones written later that were never considered when it was written. The first sibling group that needs the value to be slightly different has nowhere to go but over the top of it - a redefinition, a near-copy under another name, or a before that mutates the value back into shape. None of those read as a specification any more, and each one is a scenario nobody named.

Declaring the let in the group that reads it costs one extra line per group and buys back the naming: each group states the premises its examples start from, and a sibling that starts from a different value is a different group with its own declaration, not an override of someone else's.

This is the preventive half of Vicenzo/RSpec/NestedLetRedefinition, which reports the redefinition once it exists. Keeping the top-level group free of lets means there is nothing to redefine.

Examples:

# bad - the let reaches every example, so `#adult?` can only override it
RSpec.describe Person do
  let(:age) { 42 }

  describe '#tall?' do
    it { is_expected.to be_tall }
  end

  describe '#adult?' do
    let(:age) { 17 }

    it { is_expected.not_to be_adult }
  end
end

# good - each group declares the premises its examples start from
RSpec.describe Person do
  describe '#tall?' do
    subject(:person) { described_class.new(height: 1.75) }

    it { is_expected.to be_tall }
  end

  describe '#adult?' do
    subject(:person) { described_class.new(age: 17) }

    it { is_expected.not_to be_adult }
  end
end

a context is as good a home as a describe

# good - the premise belongs to the scenario, and the scenario is a context
RSpec.describe Person do
  describe '#adult?' do
    context 'when the person is a minor' do
      subject(:person) { described_class.new(age:) }

      let(:age) { 17 }

      it { is_expected.not_to be_adult }
    end
  end
end

Constant Summary collapse

MSG = 
'Let `:%<name>s` is declared in the top-level example group, where it reaches every ' \
'example in the file. Declare it in the group whose examples read it.'
MSG_UNNAMED = 
'A let is declared in the top-level example group, where it reaches every ' \
'example in the file. Declare it in the group whose examples read it.'

Constants included from PremiseTracking

PremiseTracking::SETUP_HOOKS

Method Summary

Methods included from TopLevelDefinition

#on_block

Methods included from PremiseTracking

#premise_name, #root_receiver_name