Class: RuboCop::Cop::RSpec::ChangeByZero

Inherits:
Base
  • Object
show all
Extended by:
AutoCorrector
Defined in:
lib/rubocop/cop/rspec/change_by_zero.rb

Overview

Prefer negated matchers over ‘to change.by(0)`.

In the case of composite expectations, cop suggest using the negation matchers of ‘RSpec::Matchers#change`.

By default the cop does not support autocorrect of compound expectations, but if you set the negated matcher for ‘change`, e.g. `not_change` with the `NegatedMatcher` option, the cop will perform the autocorrection.

Examples:

NegatedMatcher: ~ (default)

# bad
expect { run }.to change(Foo, :bar).by(0)
expect { run }.to change { Foo.bar }.by(0)

# bad - compound expectations (does not support autocorrection)
expect { run }
  .to change(Foo, :bar).by(0)
  .and change(Foo, :baz).by(0)
expect { run }
  .to change { Foo.bar }.by(0)
  .and change { Foo.baz }.by(0)

# good
expect { run }.not_to change(Foo, :bar)
expect { run }.not_to change { Foo.bar }

# good - compound expectations
define_negated_matcher :not_change, :change
expect { run }
  .to not_change(Foo, :bar)
  .and not_change(Foo, :baz)
expect { run }
  .to not_change { Foo.bar }
  .and not_change { Foo.baz }

NegatedMatcher: not_change

# bad (support autocorrection to good case)
expect { run }
  .to change(Foo, :bar).by(0)
  .and change(Foo, :baz).by(0)
expect { run }
  .to change { Foo.bar }.by(0)
  .and change { Foo.baz }.by(0)

# good
define_negated_matcher :not_change, :change
expect { run }
  .to not_change(Foo, :bar)
  .and not_change(Foo, :baz)
expect { run }
  .to not_change { Foo.bar }
  .and not_change { Foo.baz }

Constant Summary collapse

MSG = 
'Prefer `not_to change` over `to change.by(0)`.'
MSG_COMPOUND = 
'Prefer %<preferred>s with compound expectations ' \
'over `change.by(0)`.'
RESTRICT_ON_SEND = 
%i[change].freeze

Instance Method Summary collapse

Methods inherited from Base

inherited, #on_new_investigation

Methods included from RSpec::Language::NodePattern

#block_pattern, #numblock_pattern, #send_pattern

Methods included from RSpec::Language

#example?, #example_group?, #example_group_with_body?, #hook?, #include?, #let?, #rspec?, #shared_group?, #spec_group?, #subject?

Instance Method Details

#change_nodes(node) ⇒ Object 



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

def_node_search :change_nodes, <<-PATTERN
  $(send nil? :change ...)
PATTERN

#expect_change_with_arguments(node) ⇒ Object 



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# File 'lib/rubocop/cop/rspec/change_by_zero.rb', line 68

def_node_matcher :expect_change_with_arguments, <<-PATTERN
  (send
    (send nil? :change ...) :by
    (int 0))
PATTERN

#expect_change_with_block(node) ⇒ Object 



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# File 'lib/rubocop/cop/rspec/change_by_zero.rb', line 75

def_node_matcher :expect_change_with_block, <<-PATTERN
  (send
    (block
      (send nil? :change)
      (args)
      (send (...) $_)) :by
    (int 0))
PATTERN

#on_send(node) ⇒ Object 



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# File 'lib/rubocop/cop/rspec/change_by_zero.rb', line 89

def on_send(node)
  expect_change_with_arguments(node.parent) do
    check_offense(node.parent)
  end

  expect_change_with_block(node.parent.parent) do
    check_offense(node.parent.parent)
  end
end