1 files changed, 59 insertions, 0 deletions
diff --git a/rubocop/cop/rspec/env_mocking.rb b/rubocop/cop/rspec/env_mocking.rb
new file mode 100644
index 00000000000..96bd535df08
--- /dev/null
+++ b/rubocop/cop/rspec/env_mocking.rb
@@ -0,0 +1,59 @@
+# frozen_string_literal: true
+
+require 'rubocop-rspec'
+
+module RuboCop
+  module Cop
+    module RSpec
+      # Check for ENV mocking in specs.
+      # See https://docs.gitlab.com/ee/development/testing_guide/best_practices.html#persistent-in-memory-application-state
+      #
+      # @example
+      #
+      #   # bad
+      #   allow(ENV).to receive(:[]).with('FOO').and_return('bar')
+      #   allow(ENV).to receive(:fetch).with('FOO').and_return('bar')
+      #   allow(ENV).to receive(:[]).with(key).and_return(value)
+      #   allow(ENV).to receive(:[]).with(fetch_key(object)).and_return(fetch_value(object))
+      #
+      #   # good
+      #   stub_env('FOO', 'bar')
+      #   stub_env(key, value)
+      #   stub_env(fetch_key(object), fetch_value(object))
+      class EnvMocking < RuboCop::Cop::Base
+        extend RuboCop::Cop::AutoCorrector
+
+        MESSAGE = "Don't mock the ENV, use `stub_env` instead."
+
+        def_node_matcher :env_mocking?, <<~PATTERN
+        (send
+          (send nil? :allow
+            (const {nil? cbase} :ENV)
+          )
+          :to
+          (send
+            (send
+              (send nil? :receive (sym {:[] :fetch}))
+              :with $_
+            )
+            :and_return $_
+          )
+          ...
+        )
+        PATTERN
+
+        def on_send(node)
+          env_mocking?(node) do |key, value|
+            add_offense(node, message: MESSAGE) do |corrector|
+              corrector.replace(node.loc.expression, stub_env(key.source, value.source))
+            end
+          end
+        end
+
+        def stub_env(key, value)
+          "stub_env(#{key}, #{value})"
+        end
+      end
+    end
+  end
+end