Add Rubocop check to avoid using `be_success`

Prevent using `be_success` call in controller specs to avoid
getting following deprecation warning:

```
DEPRECATION WARNING: The success? predicate is deprecated and
will be removed in Rails 6.0.
Please use successful? as provided by Rack::Response::Helpers.
```

3 files changed, 97 insertions, 0 deletions

diff --git a/rubocop/cop/rspec/be_success_matcher.rb b/rubocop/cop/rspec/be_success_matcher.rb
new file mode 100644
index 00000000000..a137e2dba69
--- /dev/null
+++ b/rubocop/cop/rspec/be_success_matcher.rb
@@ -0,0 +1,50 @@
+require_relative '../../spec_helpers'
+
+module RuboCop
+  module Cop
+    module RSpec
+      # This cop checks for `be_success` usage in controller specs
+      #
+      # @example
+      #
+      #   # bad
+      #   it "responds with success" do
+      #     expect(response).to be_success
+      #   end
+      #
+      #   it { is_expected.to be_success }
+      #
+      #   # good
+      #   it "responds with success" do
+      #     expect(response).to be_successful
+      #   end
+      #
+      #   it { is_expected.to be_successful }
+      #
+      class BeSuccessMatcher < RuboCop::Cop::Cop
+        include SpecHelpers
+
+        MESSAGE = "Don't use deprecated `success?` method, use `successful?` instead.".freeze
+
+        def_node_search :expect_to_be_success?, <<~PATTERN
+          (send (send nil? :expect (send nil? ...)) :to (send nil? :be_success))
+        PATTERN
+
+        def_node_search :is_expected_to_be_success?, <<~PATTERN
+          (send (send nil? :is_expected) :to (send nil? :be_success))
+        PATTERN
+
+        def be_success_usage?(node)
+          expect_to_be_success?(node) || is_expected_to_be_success?(node)
+        end
+
+        def on_send(node)
+          return unless in_controller_spec?(node)
+          return unless be_success_usage?(node)
+
+          add_offense(node, location: :expression, message: MESSAGE)
+        end
+      end
+    end
+  end
+end
diff --git a/rubocop/rubocop.rb b/rubocop/rubocop.rb
index d1328c4eb38..c342df6d6c9 100644
--- a/rubocop/rubocop.rb
+++ b/rubocop/rubocop.rb
@@ -31,6 +31,7 @@ require_relative 'cop/migration/timestamps'
 require_relative 'cop/migration/update_column_in_batches'
 require_relative 'cop/migration/update_large_table'
 require_relative 'cop/project_path_helper'
+require_relative 'cop/rspec/be_success_matcher'
 require_relative 'cop/rspec/env_assignment'
 require_relative 'cop/rspec/factories_in_migration_specs'
 require_relative 'cop/rspec/top_level_describe_path'
diff --git a/rubocop/spec_helpers.rb b/rubocop/spec_helpers.rb
new file mode 100644
index 00000000000..b38dc3f8cdb
--- /dev/null
+++ b/rubocop/spec_helpers.rb
@@ -0,0 +1,46 @@
+module RuboCop
+  module SpecHelpers
+    SPEC_HELPERS = %w[fast_spec_helper.rb rails_helper.rb spec_helper.rb].freeze
+    MIGRATION_SPEC_DIRECTORIES = ['spec/migrations', 'spec/lib/gitlab/background_migration'].freeze
+    CONTROLLER_SPEC_DIRECTORIES = ['spec/controllers', 'spec/support/shared_examples/controllers'].freeze
+
+    # Returns true if the given node originated from the spec directory.
+    def in_spec?(node)
+      path = node.location.expression.source_buffer.name
+      pwd = RuboCop::PathUtil.pwd
+
+      !SPEC_HELPERS.include?(File.basename(path)) &&
+        path.start_with?(File.join(pwd, 'spec'), File.join(pwd, 'ee', 'spec'))
+    end
+
+    def migration_directories
+      @migration_directories ||= MIGRATION_SPEC_DIRECTORIES.map do |dir|
+        pwd = RuboCop::PathUtil.pwd
+        [File.join(pwd, dir), File.join(pwd, 'ee', dir)]
+      end.flatten
+    end
+
+    # Returns true if the given node originated from a migration spec.
+    def in_migration_spec?(node)
+      path = node.location.expression.source_buffer.name
+
+      in_spec?(node) &&
+        path.start_with?(*migration_directories)
+    end
+
+    def controller_directories
+      @controller_directories ||= CONTROLLER_SPEC_DIRECTORIES.map do |dir|
+        pwd = RuboCop::PathUtil.pwd
+        [File.join(pwd, dir), File.join(pwd, 'ee', dir)]
+      end.flatten
+    end
+
+    # Returns true if the given node originated from a controller spec.
+    def in_controller_spec?(node)
+      path = node.location.expression.source_buffer.name
+
+      in_spec?(node) &&
+        path.start_with?(*controller_directories)
+    end
+  end
+end