Merge pull request #1239 from rubocop/add-be-nil-cop

Add new `RSpec/BeNil` cop

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## Master (Unreleased)
 
+* Add new `RSpec/BeNil` cop. ([@bquorning][])
+
 ## 2.8.0 (2022-01-24)
 
 * Fix `RSpec/FactoryBot/SyntaxMethods` and `RSpec/Capybara/FeatureMethods` to inspect shared groups. ([@pirj][])

config/default.yml

@@ -148,6 +148,12 @@ RSpec/BeEql:
   VersionAdded: '1.7'
   Reference: https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/BeEql
 
+RSpec/BeNil:
+  Description: Check that `be_nil` is used instead of `be(nil)`.
+  Enabled: pending
+  VersionAdded: 2.9.0
+  Reference: https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/BeNil
+
 RSpec/BeforeAfterAll:
   Description: Check that before/after(:all) isn't being used.
   Enabled: true

docs/modules/ROOT/pages/cops.adoc

@@ -8,6 +8,7 @@
 * xref:cops_rspec.adoc#rspecaroundblock[RSpec/AroundBlock]
 * xref:cops_rspec.adoc#rspecbe[RSpec/Be]
 * xref:cops_rspec.adoc#rspecbeeql[RSpec/BeEql]
+* xref:cops_rspec.adoc#rspecbenil[RSpec/BeNil]
 * xref:cops_rspec.adoc#rspecbeforeafterall[RSpec/BeforeAfterAll]
 * xref:cops_rspec.adoc#rspeccontextmethod[RSpec/ContextMethod]
 * xref:cops_rspec.adoc#rspeccontextwording[RSpec/ContextWording]

docs/modules/ROOT/pages/cops_rspec.adoc

@@ -237,6 +237,38 @@ expect(foo).to be(nil)
 
 * https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/BeEql
 
+== RSpec/BeNil
+
+|===
+| Enabled by default | Safe | Supports autocorrection | Version Added | Version Changed
+
+| Pending
+| Yes
+| Yes
+| 2.9.0
+| -
+|===
+
+Check that `be_nil` is used instead of `be(nil)`.
+
+RSpec has a built-in `be_nil` matcher specifically for expecting `nil`.
+For consistent specs, we recommend using that instead of `be(nil).
+
+=== Examples
+
+[source,ruby]
+----
+# bad
+expect(foo).to be(nil)
+
+# good
+expect(foo).to be_nil
+----
+
+=== References
+
+* https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/BeNil
+
 == RSpec/BeforeAfterAll
 
 |===

lib/rubocop/cop/rspec/be_nil.rb

@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module RSpec
+      # Check that `be_nil` is used instead of `be(nil)`.
+      #
+      # RSpec has a built-in `be_nil` matcher specifically for expecting `nil`.
+      # For consistent specs, we recommend using that instead of `be(nil).
+      #
+      # @example
+      #
+      #   # bad
+      #   expect(foo).to be(nil)
+      #
+      #   # good
+      #   expect(foo).to be_nil
+      #
+      class BeNil < Base
+        extend AutoCorrector
+
+        MSG = 'Prefer `be_nil` over `be(nil)`.'
+        RESTRICT_ON_SEND = %i[be].freeze
+
+        # @!method nil_value_expectation?(node)
+        def_node_matcher :nil_value_expectation?, <<-PATTERN
+          (send nil? :be nil)
+        PATTERN
+
+        def on_send(node)
+          return unless nil_value_expectation?(node)
+
+          add_offense(node) do |corrector|
+            corrector.replace(node.loc.expression, 'be_nil')
+          end
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/rspec_cops.rb

@@ -22,6 +22,7 @@
 require_relative 'rspec/around_block'
 require_relative 'rspec/be'
 require_relative 'rspec/be_eql'
+require_relative 'rspec/be_nil'
 require_relative 'rspec/before_after_all'
 require_relative 'rspec/context_method'
 require_relative 'rspec/context_wording'

spec/rubocop/cop/rspec/be_nil_spec.rb

@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::RSpec::BeNil do
+  it 'registers an offense when using `#be` for `nil` value' do
+    expect_offense(<<~RUBY)
+      expect(foo).to be(nil)
+                     ^^^^^^^ Prefer `be_nil` over `be(nil)`.
+    RUBY
+
+    expect_correction(<<~RUBY)
+      expect(foo).to be_nil
+    RUBY
+  end
+
+  it 'does not register an offense when using `#be_nil`' do
+    expect_no_offenses(<<~RUBY)
+      expect(foo).to be_nil
+    RUBY
+  end
+
+  it 'does not register an offense when using `#be` with other values' do
+    expect_no_offenses(<<~RUBY)
+      expect(foo).to be(true)
+      expect(foo).to be(false)
+      expect(foo).to be(1)
+      expect(foo).to be("yes")
+      expect(foo).to be(Class.new)
+    RUBY
+  end
+end