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Latest commit c7f63ad May 12, 2017 @geoffharcourt geoffharcourt Version 0.2.0
- allow nested calls to `ClimateControl.modify` within the same thread

Climate Control

Easily manage your environment.


Add this line to your application's Gemfile:

gem 'climate_control'

And then execute:

$ bundle

Or install it yourself as:

$ gem install climate_control


Climate Control can be used to temporarily assign environment variables within a block:

ClimateControl.modify CONFIRMATION_INSTRUCTIONS_BCC: '' do
  sign_up_as ''
  confirm_account_for_email ''
  current_email.should bcc_to('')

To use with RSpec, you could define this in your spec:

def with_modified_env(options, &block)
  ClimateControl.modify(options, &block)

This would allow for more straightforward way to modify the environment:

require 'spec_helper'

describe Thing, 'name' do
  it 'appends ADDITIONAL_NAME' do
    with_modified_env ADDITIONAL_NAME: 'bar' do
      expect( eq('John Doe Bar')

  def with_modified_env(options, &block)
    ClimateControl.modify(options, &block)

To modify the environment for an entire set of tests in RSpec, use an around block:

describe Thing, 'name' do
  # ... tests

  around do |example|
    ClimateControl.modify FOO: 'bar' do

Environment variables assigned within the block will be preserved; essentially, the code should behave exactly the same with and without the block, except for the overrides. Transparency is crucial because the code executed within the block is not for ClimateControl to manage or modify. See the tests for more detail about the specific behaviors.

Why Use Climate Control?

By following guidelines regarding environment variables outlined by the twelve-factor app, testing code in an isolated manner becomes more difficult:

  • avoiding modifications and testing values, we introduce mystery guests
  • making modifications and testing values, we introduce risk as environment variables represent global state

Climate Control modifies environment variables only within the context of the block, ensuring values are managed properly and consistently.


  1. Fork it
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create new Pull Request


climate_control is copyright 2012-2017 Joshua Clayton and thoughtbot, inc. It is free software and may be redistributed under the terms specified in the LICENSE.txt file.