1 files changed, 58 insertions, 0 deletions
diff --git a/rubocop/cop/rspec/env_assignment.rb b/rubocop/cop/rspec/env_assignment.rb
new file mode 100644
index 00000000000..257454af0e1
--- /dev/null
+++ b/rubocop/cop/rspec/env_assignment.rb
@@ -0,0 +1,58 @@
+require 'rubocop-rspec'
+require_relative '../../spec_helpers'
+
+module RuboCop
+  module Cop
+    module RSpec
+      # This cop checks for ENV assignment in specs
+      #
+      # @example
+      #
+      #   # bad
+      #   before do
+      #     ENV['FOO'] = 'bar'
+      #   end
+      #
+      #   # good
+      #   before do
+      #     stub_env('FOO', 'bar')
+      #   end
+      class EnvAssignment < Cop
+        include SpecHelpers
+
+        MESSAGE = "Don't assign to ENV, use `stub_env` instead.".freeze
+
+        def_node_search :env_assignment?, <<~PATTERN
+          (send (const nil? :ENV) :[]= ...)
+        PATTERN
+
+        # Following is what node.children looks like on a match
+        # [s(:const, nil, :ENV), :[]=, s(:str, "key"), s(:str, "value")]
+        def on_send(node)
+          return unless in_spec?(node)
+          return unless env_assignment?(node)
+
+          add_offense(node, :expression, MESSAGE)
+        end
+
+        def autocorrect(node)
+          lambda do |corrector|
+            corrector.replace(node.loc.expression, stub_env(env_key(node), env_value(node)))
+          end
+        end
+
+        def env_key(node)
+          node.children[2].source
+        end
+
+        def env_value(node)
+          node.children[3].source
+        end
+
+        def stub_env(key, value)
+          "stub_env(#{key}, #{value})"
+        end
+      end
+    end
+  end
+end