Add a custom RSpec/SingleLineHook cop

This cop adds an offense when `before`, `after`, or `around` are used as
single-line blocks.

2 files changed, 37 insertions, 0 deletions

diff --git a/rubocop/cop/rspec/single_line_hook.rb b/rubocop/cop/rspec/single_line_hook.rb
new file mode 100644
index 00000000000..a156b1d34cf
--- /dev/null
+++ b/rubocop/cop/rspec/single_line_hook.rb
@@ -0,0 +1,36 @@
+module RuboCop
+  module Cop
+    module RSpec
+      # This cop checks for single-line hook blocks
+      #
+      # @example
+      #
+      #   # bad
+      #   before { do_something }
+      #   after(:each) { undo_something }
+      #
+      #   # good
+      #   before do
+      #     do_something
+      #   end
+      #
+      #   after(:each) do
+      #     undo_something
+      #   end
+      class SingleLineHook < RuboCop::Cop::RSpec::Cop
+        MESSAGE = "Don't use single-line hook blocks.".freeze
+
+        def_node_search :rspec_hook?, <<~PATTERN
+          (send nil {:after :around :before} ...)
+        PATTERN
+
+        def on_block(node)
+          return unless rspec_hook?(node)
+          return unless node.single_line?
+
+          add_offense(node, :expression, MESSAGE)
+        end
+      end
+    end
+  end
+end
diff --git a/rubocop/rubocop.rb b/rubocop/rubocop.rb
index 6b8d127dde6..55d7708fa8c 100644
--- a/rubocop/rubocop.rb
+++ b/rubocop/rubocop.rb
@@ -15,3 +15,4 @@ require_relative 'cop/migration/remove_index'
 require_relative 'cop/migration/reversible_add_column_with_default'
 require_relative 'cop/migration/timestamps'
 require_relative 'cop/migration/update_column_in_batches'
+require_relative 'cop/rspec/single_line_hook'