Add new RSpec/EmptyHook cop

Closes #811

CHANGELOG.md

@@ -5,6 +5,7 @@
 * Fix `RSpec/FilePath` detection when absolute path includes test subject. ([@eitoball][])
 * Add new `Capybara/VisibilityMatcher` cop. ([@aried3r][])
 * Ignore String constants by `RSpec/Describe`. ([@AlexWayfer][])
+* Add new `RSpec/EmptyHook` cop. ([@tejasbubane][])
 
 ## 1.38.1 (2020-02-15)
 
@@ -496,3 +497,4 @@ Compatibility release so users can upgrade RuboCop to 0.51.0. No new features.
 [@eitoball]: https://github.com/eitoball
 [@aried3r]: https://github.com/aried3r
 [@AlexWayfer]: https://github.com/AlexWayfer
+[@tejasbubane]: https://github.com/tejasbubane

config/default.yml

@@ -105,6 +105,12 @@ RSpec/EmptyExampleGroup:
   CustomIncludeMethods: []
   StyleGuide: https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/EmptyExampleGroup
 
+RSpec/EmptyHook:
+  Description: Checks for empty before and after hooks.
+  Enabled: true
+  VersionAdded: 1.38.2
+  StyleGuide: https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/EmptyHook
+
 RSpec/EmptyLineAfterExample:
   Description: Checks if there is an empty line after example blocks.
   Enabled: true

lib/rubocop/cop/rspec/empty_hook.rb

@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+module RuboCop
+  module Cop
+    module RSpec
+      #  Checks for empty before and after hooks.
+      #
+      # @example
+      #   # bad
+      #   before {}
+      #   after do; end
+      #   before(:all) do
+      #   end
+      #   all(:all) { nil }
+      #
+      #   # good
+      #   before { create_users }
+      #   after do; cleanup_users; end
+      #   before(:all) do
+      #     create_feed
+      #   end
+      #   all(:all) { cleanup_feed }
+      class EmptyHook < Cop
+        MSG = 'Empty hook detected.'
+
+        def_node_matcher :empty_hook?, <<~PATTERN
+          (block
+            $(send nil? {:before :after}
+              (sym {:each :all :suite})?)
+            _ {(:nil) nil?})
+        PATTERN
+
+        def on_block(node)
+          empty_hook?(node) do |hook|
+            add_offense(hook)
+          end
+        end
+      end
+    end
+  end
+end

lib/rubocop/cop/rspec_cops.rb

@@ -30,6 +30,7 @@
 require_relative 'rspec/described_class_module_wrapping'
 require_relative 'rspec/dialect'
 require_relative 'rspec/empty_example_group'
+require_relative 'rspec/empty_hook'
 require_relative 'rspec/empty_line_after_example'
 require_relative 'rspec/empty_line_after_example_group'
 require_relative 'rspec/empty_line_after_final_let'

manual/cops.md

@@ -29,6 +29,7 @@
 * [RSpec/DescribedClassModuleWrapping](cops_rspec.md#rspecdescribedclassmodulewrapping)
 * [RSpec/Dialect](cops_rspec.md#rspecdialect)
 * [RSpec/EmptyExampleGroup](cops_rspec.md#rspecemptyexamplegroup)
+* [RSpec/EmptyHook](cops_rspec.md#rspecemptyhook)
 * [RSpec/EmptyLineAfterExample](cops_rspec.md#rspecemptylineafterexample)
 * [RSpec/EmptyLineAfterExampleGroup](cops_rspec.md#rspecemptylineafterexamplegroup)
 * [RSpec/EmptyLineAfterFinalLet](cops_rspec.md#rspecemptylineafterfinallet)

manual/cops_rspec.md

@@ -639,6 +639,43 @@ CustomIncludeMethods | `[]` | Array
 
 * [https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/EmptyExampleGroup](https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/EmptyExampleGroup)
 
+## RSpec/EmptyHook
+
+Enabled by default | Supports autocorrection
+--- | ---
+Enabled | No
+
+Checks for empty before and after hooks.
+
+### Examples
+
+```ruby
+# bad
+before {}
+after do; end
+before(:all) do
+end
+all(:all) { nil }
+
+# good
+before { create_users }
+after do; cleanup_users; end
+before(:all) do
+  create_feed
+end
+all(:all) { cleanup_feed }
+```
+
+### Configurable attributes
+
+Name | Default value | Configurable values
+--- | --- | ---
+VersionAdded | `1.38.2` | String
+
+### References
+
+* [https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/EmptyHook](https://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/EmptyHook)
+
 ## RSpec/EmptyLineAfterExample
 
 Enabled by default | Supports autocorrection

spec/rubocop/cop/rspec/empty_hook_spec.rb

@@ -0,0 +1,76 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::RSpec::EmptyHook do
+  subject(:cop) { described_class.new(config) }
+
+  let(:config) { RuboCop::Config.new }
+
+  shared_examples 'empty hook' do |hook_type|
+    it 'registers offense with empty block' do
+      expect_offense(<<~RUBY)
+        #{hook_type} {}
+        #{'^' * hook_type.length} Empty hook detected.
+      RUBY
+    end
+
+    it 'registers offense with empty single-line do-end' do
+      expect_offense(<<~RUBY)
+        #{hook_type} do; end
+        #{'^' * hook_type.length} Empty hook detected.
+      RUBY
+    end
+
+    it 'registers offense with empty multi-line do-end' do
+      expect_offense(<<~RUBY)
+        #{hook_type} do
+        #{'^' * hook_type.length} Empty hook detected.
+        end
+      RUBY
+    end
+
+    it 'registers offense with empty single-line nil' do
+      expect_offense(<<~RUBY)
+        #{hook_type} { nil }
+        #{'^' * hook_type.length} Empty hook detected.
+      RUBY
+    end
+
+    it 'registers offense with empty multi-line nil' do
+      expect_offense(<<~RUBY)
+        #{hook_type} do
+        #{'^' * hook_type.length} Empty hook detected.
+          nil
+        end
+      RUBY
+    end
+
+    it 'allows single-line non-empty blocks' do
+      expect_no_offenses(<<~RUBY)
+        #{hook_type} { create_users }
+      RUBY
+    end
+
+    it 'allows multi-line non-empty blocks' do
+      expect_no_offenses(<<~RUBY)
+        #{hook_type} do
+          create_users
+          create_businesses
+        end
+      RUBY
+    end
+  end
+
+  context 'with before hooks' do
+    it_behaves_like 'empty hook', 'before'
+    it_behaves_like 'empty hook', 'before(:each)'
+    it_behaves_like 'empty hook', 'before(:suite)'
+    it_behaves_like 'empty hook', 'before(:all)'
+  end
+
+  context 'with after hooks' do
+    it_behaves_like 'empty hook', 'after'
+    it_behaves_like 'empty hook', 'after(:each)'
+    it_behaves_like 'empty hook', 'after(:suite)'
+    it_behaves_like 'empty hook', 'after(:all)'
+  end
+end