Add new RSpec/NegatedExpectation cop

This cop checks for expectations with `!`.
The autocorrection is marked as unsafe, because it may change the expectation from a positive to a negative one, or vice versa.

```ruby
!expect(foo).to be_valid

expect(foo).not_to be_valid
```

.rubocop.yml

@@ -171,6 +171,8 @@ RSpec/MatchArray:
   Enabled: true
 RSpec/MetadataStyle:
   Enabled: true
+RSpec/NegatedExpectation:
+  Enabled: true
 RSpec/NoExpectationExample:
   Enabled: true
 RSpec/PendingWithoutReason:

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## Master (Unreleased)
 
+- Add new `RSpec/NegatedExpectation` cop. ([@ydah])
+
 ## 2.27.1 (2024-03-03)
 
 - Fix a false positive for `RSpec/RepeatedSubjectCall` when `subject.method_call`. ([@ydah])

config/default.yml

@@ -692,6 +692,13 @@ RSpec/NamedSubject:
   StyleGuide: https://rspec.rubystyle.guide/#use-subject
   Reference: https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/NamedSubject
 
+RSpec/NegatedExpectation:
+  Description: Checks for expectations with `!`.
+  Enabled: pending
+  SafeAutoCorrect: false
+  VersionAdded: "<<next>>"
+  Reference: https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/NegatedExpectation
+
 RSpec/NestedGroups:
   Description: Checks for nested example groups.
   Enabled: true

docs/modules/ROOT/pages/cops.adoc

@@ -70,6 +70,7 @@
 * xref:cops_rspec.adoc#rspecmultiplememoizedhelpers[RSpec/MultipleMemoizedHelpers]
 * xref:cops_rspec.adoc#rspecmultiplesubjects[RSpec/MultipleSubjects]
 * xref:cops_rspec.adoc#rspecnamedsubject[RSpec/NamedSubject]
+* xref:cops_rspec.adoc#rspecnegatedexpectation[RSpec/NegatedExpectation]
 * xref:cops_rspec.adoc#rspecnestedgroups[RSpec/NestedGroups]
 * xref:cops_rspec.adoc#rspecnoexpectationexample[RSpec/NoExpectationExample]
 * xref:cops_rspec.adoc#rspecnottonot[RSpec/NotToNot]

docs/modules/ROOT/pages/cops_rspec.adoc

@@ -3888,6 +3888,40 @@ end
 * https://rspec.rubystyle.guide/#use-subject
 * https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/NamedSubject
 
+== RSpec/NegatedExpectation
+
+|===
+| Enabled by default | Safe | Supports autocorrection | Version Added | Version Changed
+
+| Pending
+| Yes
+| Always (Unsafe)
+| <<next>>
+| -
+|===
+
+Checks for expectations with `!`.
+
+=== Safety
+
+The autocorrection is marked as unsafe, because it may change the
+expectation from a positive to a negative one, or vice versa.
+
+=== Examples
+
+[source,ruby]
+----
+# bad
+!expect(foo).to be_valid
+
+# good
+expect(foo).not_to be_valid
+----
+
+=== References
+
+* https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/NegatedExpectation
+
 == RSpec/NestedGroups
 
 |===

lib/rubocop/cop/rspec/negated_expectation.rb

@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module RSpec
+      # Checks for expectations with `!`.
+      #
+      # @safety
+      #   The autocorrection is marked as unsafe, because it may change the
+      #   expectation from a positive to a negative one, or vice versa.
+      #
+      # @example
+      #   # bad
+      #   !expect(foo).to be_valid
+      #
+      #   # good
+      #   expect(foo).not_to be_valid
+      #
+      class NegatedExpectation < Base
+        extend AutoCorrector
+
+        MSG = 'Use `expect(...).%<replaced>s` instead of ' \
+              '`!expect(...)`.%<runner>s'
+        RESTRICT_ON_SEND = Runners.all
+
+        def on_send(node)
+          return unless node.parent&.send_type?
+          return unless node.parent.method?(:!)
+
+          replaced = replaced(node)
+          add_offense(node.parent,
+                      message: message(node, replaced)) do |corrector|
+            corrector.remove(node.parent.loc.selector)
+            corrector.replace(node.loc.selector, replaced)
+          end
+        end
+
+        private
+
+        def message(node, replaced)
+          format(MSG, runner: node.loc.selector.source, replaced: replaced)
+        end
+
+        def replaced(node)
+          runner = node.loc.selector.source
+          runner == 'to' ? 'not_to' : 'to'
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/rspec_cops.rb

@@ -96,6 +96,7 @@
 require_relative 'rspec/multiple_memoized_helpers'
 require_relative 'rspec/multiple_subjects'
 require_relative 'rspec/named_subject'
+require_relative 'rspec/negated_expectation'
 require_relative 'rspec/nested_groups'
 require_relative 'rspec/no_expectation_example'
 require_relative 'rspec/not_to_not'

spec/rubocop/cop/rspec/negated_expectations_spec.rb

@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::RSpec::NegatedExpectation, :config do
+  it 'registers an offense when using redundant negation with `.to`' do
+    expect_offense(<<~RUBY)
+      !expect(foo).to be_valid
+      ^^^^^^^^^^^^^^^^^^^^^^^^ Use `expect(...).not_to` instead of `!expect(...)`.to
+    RUBY
+
+    expect_correction(<<~RUBY)
+      expect(foo).not_to be_valid
+    RUBY
+  end
+
+  it 'registers an offense when using redundant negation with `.not_to`' do
+    expect_offense(<<~RUBY)
+      !expect(foo).not_to be_valid
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `expect(...).to` instead of `!expect(...)`.not_to
+    RUBY
+
+    expect_correction(<<~RUBY)
+      expect(foo).to be_valid
+    RUBY
+  end
+
+  it 'registers an offense when using redundant negation with `.to_not`' do
+    expect_offense(<<~RUBY)
+      !expect(foo).to_not be_valid
+      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Use `expect(...).to` instead of `!expect(...)`.to_not
+    RUBY
+
+    expect_correction(<<~RUBY)
+      expect(foo).to be_valid
+    RUBY
+  end
+
+  it 'does not register an offense when without redundant negation' do
+    expect_no_offenses(<<~RUBY)
+      expect(foo).not_to be_valid
+    RUBY
+  end
+end