Class: RuboCop::Cop::Vicenzo::RSpec::MutatedPremises

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

Overview

Do not mutate the premises of an example.

A let, let_it_be or subject is the premise a reader assumes true when reading the file. Mutating it somewhere else breaks that in two ways:

  1. The file lies. You read let(:params) { { name: 'Ada' } }, run it, and the value is different — the explanation is a before dozens of lines away.
  2. It breeds flakiness. let is lazy, so whichever example materialises it first decides the final state. A context that touches the premises in another order silently changes the result.

Persisting changes while building a premise is flagged wherever it happens inside the definition, including inline forms such as tap, because a factory trait or transient is always available instead. Collection mutations and attribute writers are flagged when they change a premise declared in an ancestor group, so building a local value inside the definition itself stays allowed.

Examples are not inspected: there the mutation usually is the behaviour under test.

Examples:

# bad — persisting while building the premise

let(:order) { create(:order).tap { |record| record.update!(status: :shipped) } }

# bad — the same laziness spelled out

let(:order) do
  order = create(:order)
  order.update_column(:status, :shipped)
  order
end

# good — the factory owns it

let(:order) { create(:order, :shipped) }
# bad — the hook rewrites the premise

let(:params) { { name: 'Ada' } }
before { params[:age] = 10 }

# bad — patching a record the premise built

before { order.shipment.update!(carrier:) }

# good — each context declares its complete premise

context 'when the age is informed' do
  let(:params) { { name: 'Ada', age: 10 } }
end

# good — creation order lets the production code do the wiring

before do
  carrier
  order
end
# good — local builder, the value is born and dies inside the premise

let(:csv_content) { CSV.generate { |csv| csv << header } }

Constant Summary collapse

MSG_MUTATION = 
'Do not mutate the premise `%<name>s`. Declare the final state where it is needed — ' \
'factory trait, factory transient, or creation order.'
MSG_PERSISTENCE = 
'Do not persist changes while building `%<name>s`. Move it to a factory ' \
'trait/transient, or declare the final state in the context that needs it.'
PERSISTENCE_METHODS = 
%i[
  update update! update_attribute update_column update_columns save save! destroy destroy! touch
  increment! decrement! toggle!
].freeze
COLLECTION_METHODS = 
%i[<< push concat unshift store merge! deep_merge! clear delete].freeze

Constants included from PremiseTracking

PremiseTracking::SETUP_HOOKS

Instance Method Summary collapse

Methods included from PremiseTracking

#premise_name, #root_receiver_name

Instance Method Details

#on_block(node) ⇒ Object Also known as: on_numblock 



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# File 'lib/rubocop/cop/vicenzo/rspec/mutated_premises.rb', line 85

def on_block(node)
  return unless example_group?(node) && outermost_example_group?(node)

  walk_example_group(node, all_premises(node))
end