diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
new file mode 100644
index 0000000..d2b715e
--- /dev/null
+++ b/.github/workflows/main.yml
@@ -0,0 +1,30 @@
+name: Ruby
+
+on:
+  push:
+    branches:
+      - main
+
+  pull_request:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    name: Ruby ${{ matrix.ruby }}
+    strategy:
+      matrix:
+        ruby:
+          - '3.3.4'
+          - '3.2.5'
+          - '3.1.6'
+          - '3.0.7'
+
+    steps:
+    - uses: actions/checkout@v4
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby }}
+        bundler-cache: true
+    - name: Run the default task
+      run: bundle exec rake
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..9106b2a
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,8 @@
+/.bundle/
+/.yardoc
+/_yardoc/
+/coverage/
+/doc/
+/pkg/
+/spec/reports/
+/tmp/
diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
index 0000000..d4c8700
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,5 @@
+## [Unreleased]
+
+## [0.1.0] - 2024-08-11
+
+- Initial release
diff --git a/CODE_OF_CONDUCT.md b/CODE_OF_CONDUCT.md
new file mode 100644
index 0000000..67fe8ce
--- /dev/null
+++ b/CODE_OF_CONDUCT.md
@@ -0,0 +1,132 @@
+# Contributor Covenant Code of Conduct
+
+## Our Pledge
+
+We as members, contributors, and leaders pledge to make participation in our
+community a harassment-free experience for everyone, regardless of age, body
+size, visible or invisible disability, ethnicity, sex characteristics, gender
+identity and expression, level of experience, education, socio-economic status,
+nationality, personal appearance, race, caste, color, religion, or sexual
+identity and orientation.
+
+We pledge to act and interact in ways that contribute to an open, welcoming,
+diverse, inclusive, and healthy community.
+
+## Our Standards
+
+Examples of behavior that contributes to a positive environment for our
+community include:
+
+* Demonstrating empathy and kindness toward other people
+* Being respectful of differing opinions, viewpoints, and experiences
+* Giving and gracefully accepting constructive feedback
+* Accepting responsibility and apologizing to those affected by our mistakes,
+  and learning from the experience
+* Focusing on what is best not just for us as individuals, but for the overall
+  community
+
+Examples of unacceptable behavior include:
+
+* The use of sexualized language or imagery, and sexual attention or advances of
+  any kind
+* Trolling, insulting or derogatory comments, and personal or political attacks
+* Public or private harassment
+* Publishing others' private information, such as a physical or email address,
+  without their explicit permission
+* Other conduct which could reasonably be considered inappropriate in a
+  professional setting
+
+## Enforcement Responsibilities
+
+Community leaders are responsible for clarifying and enforcing our standards of
+acceptable behavior and will take appropriate and fair corrective action in
+response to any behavior that they deem inappropriate, threatening, offensive,
+or harmful.
+
+Community leaders have the right and responsibility to remove, edit, or reject
+comments, commits, code, wiki edits, issues, and other contributions that are
+not aligned to this Code of Conduct, and will communicate reasons for moderation
+decisions when appropriate.
+
+## Scope
+
+This Code of Conduct applies within all community spaces, and also applies when
+an individual is officially representing the community in public spaces.
+Examples of representing our community include using an official email address,
+posting via an official social media account, or acting as an appointed
+representative at an online or offline event.
+
+## Enforcement
+
+Instances of abusive, harassing, or otherwise unacceptable behavior may be
+reported to the community leaders responsible for enforcement at
+[INSERT CONTACT METHOD].
+All complaints will be reviewed and investigated promptly and fairly.
+
+All community leaders are obligated to respect the privacy and security of the
+reporter of any incident.
+
+## Enforcement Guidelines
+
+Community leaders will follow these Community Impact Guidelines in determining
+the consequences for any action they deem in violation of this Code of Conduct:
+
+### 1. Correction
+
+**Community Impact**: Use of inappropriate language or other behavior deemed
+unprofessional or unwelcome in the community.
+
+**Consequence**: A private, written warning from community leaders, providing
+clarity around the nature of the violation and an explanation of why the
+behavior was inappropriate. A public apology may be requested.
+
+### 2. Warning
+
+**Community Impact**: A violation through a single incident or series of
+actions.
+
+**Consequence**: A warning with consequences for continued behavior. No
+interaction with the people involved, including unsolicited interaction with
+those enforcing the Code of Conduct, for a specified period of time. This
+includes avoiding interactions in community spaces as well as external channels
+like social media. Violating these terms may lead to a temporary or permanent
+ban.
+
+### 3. Temporary Ban
+
+**Community Impact**: A serious violation of community standards, including
+sustained inappropriate behavior.
+
+**Consequence**: A temporary ban from any sort of interaction or public
+communication with the community for a specified period of time. No public or
+private interaction with the people involved, including unsolicited interaction
+with those enforcing the Code of Conduct, is allowed during this period.
+Violating these terms may lead to a permanent ban.
+
+### 4. Permanent Ban
+
+**Community Impact**: Demonstrating a pattern of violation of community
+standards, including sustained inappropriate behavior, harassment of an
+individual, or aggression toward or disparagement of classes of individuals.
+
+**Consequence**: A permanent ban from any sort of public interaction within the
+community.
+
+## Attribution
+
+This Code of Conduct is adapted from the [Contributor Covenant][homepage],
+version 2.1, available at
+[https://www.contributor-covenant.org/version/2/1/code_of_conduct.html][v2.1].
+
+Community Impact Guidelines were inspired by
+[Mozilla's code of conduct enforcement ladder][Mozilla CoC].
+
+For answers to common questions about this code of conduct, see the FAQ at
+[https://www.contributor-covenant.org/faq][FAQ]. Translations are available at
+[https://www.contributor-covenant.org/translations][translations].
+
+[homepage]: https://www.contributor-covenant.org
+[v2.1]: https://www.contributor-covenant.org/version/2/1/code_of_conduct.html
+[Mozilla CoC]: https://github.com/mozilla/diversity
+[FAQ]: https://www.contributor-covenant.org/faq
+[translations]: https://www.contributor-covenant.org/translations
diff --git a/Gemfile b/Gemfile
new file mode 100644
index 0000000..54014c7
--- /dev/null
+++ b/Gemfile
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+source 'https://rubygems.org'
+
+# Specify your gem's dependencies in loadout.gemspec
+gemspec
+
+gem 'rake', '~> 13.0'
+gem 'minitest', '~> 5.16'
diff --git a/Gemfile.lock b/Gemfile.lock
new file mode 100644
index 0000000..6b3b36d
--- /dev/null
+++ b/Gemfile.lock
@@ -0,0 +1,22 @@
+PATH
+  remote: .
+  specs:
+    loadout (0.1.0)
+
+GEM
+  remote: https://rubygems.org/
+  specs:
+    minitest (5.24.1)
+    rake (13.2.1)
+
+PLATFORMS
+  arm64-darwin-23
+  ruby
+
+DEPENDENCIES
+  loadout!
+  minitest (~> 5.16)
+  rake (~> 13.0)
+
+BUNDLED WITH
+   2.5.17
diff --git a/LICENSE.txt b/LICENSE.txt
new file mode 100644
index 0000000..9775326
--- /dev/null
+++ b/LICENSE.txt
@@ -0,0 +1,21 @@
+The MIT License (MIT)
+
+Copyright (c) 2024 Max Chernyak
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..1a4d0d1
--- /dev/null
+++ b/README.md
@@ -0,0 +1,227 @@
+# Loadout
+
+Rails vanilla config is good enough, but tends to get messy. This gem provides a few helpers to
+
+- Reduce repetition
+- Raise error when required ENV vars or credentials are unset
+- Parse reasonable ENV values into booleans, integers, floats, and arrays
+
+## Synopsis
+
+```ruby
+Rails.application.configure do
+  extend Loadout::Helpers
+
+  config.some_secret = cred(:secret) { 'default' }
+  config.value_from_env_or_cred = env.cred(:key_name)
+
+  prefix(:service) do
+    config.x.service.optional_string = env.cred(:api_key) { 'default_key' }
+    config.x.service.required_string = env.cred(:api_secret)
+
+    config.x.service.optional_bool   = bool.env(:bool_flag) { false }
+    config.x.service.number          = int.env.cred(:number) { nil }
+    config.x.service.float           = float.env.cred(:number)
+    config.x.service.array           = list.env(:comma_list)
+  end
+end
+```
+
+## Installation
+
+Note: this gem requires Ruby 3.
+
+Install the gem and add to the application's Gemfile by executing:
+
+    $ bundle add loadout
+
+If bundler is not being used to manage dependencies, install the gem by executing:
+
+    $ gem install loadout
+
+## Usage
+
+1. Include helpers into your `config/application.rb` and `config/environments/*.rb`:
+
+    ```ruby
+    extend Loadout::Helpers
+    ```
+
+    This should be done in each file where you'd like to use loadout.
+
+2. Grab a value from credentials:
+
+    ```ruby
+    config.key = cred(:key_name)
+    ```
+
+3. Or from ENV:
+
+    ```ruby
+    config.key = env(:key_name)
+    ```
+
+4. Or whichever one is found first:
+
+    ```ruby
+    config.key = env.cred(:key_name)
+    ```
+
+5. Or the other way around:
+
+    ```ruby
+    config.key = cred.env(:key_name)
+    ```
+
+6. If it's a nested credential value, you can supply multiple keys:
+
+    ```ruby
+    # Look up service.key_name in credentials
+    config.key = cred(:service, :key_name)
+    ```
+
+7. It will do the right thing if you also add env:
+
+    ```ruby
+    # Look up service.key_name in credentials, or SERVICE_KEY_NAME in ENV
+    config.key = cred.env(:service, :key_name)
+    ```
+
+8. Parse ENV value into a boolean:
+
+    ```ruby
+    # Valid true strings: 1/y/yes/t/true
+    # Valid false strings: "" or 0/n/no/f/false
+    # (case insensitive)
+    #
+    # Any other string will raise an error.
+    config.some_flag = bool.cred.env(:key_name)
+    ```
+
+    Note: because credentials come from YAML, they don't need to be parsed. Only ENV values are parsed.
+
+9. Integers and floats are also supported:
+
+    ```ruby
+    config.some_int   = int.cred.env(:int_key_name)
+    config.some_float = float.cred.env(:float_key_name)
+    ```
+
+10. Lists are supported too:
+
+    ```ruby
+    # Parses strings like "foo, bar, baz", "foo|bar|baz", "foo bar baz" into ['foo', 'bar', 'baz']
+    config.some_list = list.cred.env(:key_name)
+    ```
+
+11. You can set your own list separator (string or regex):
+
+    ```ruby
+    # Parses 'foo0bar0baz' as ['foo', 'bar', 'baz']
+    config.some_list = list('0').env(:key_name)
+    ```
+
+12. Use a block at the end to specify a default value:
+
+    ```ruby
+    config.some_list = list.cred.env(:key_name) { ['default'] }
+    ```
+
+13. Use prefix to avoid repeating the same nesting:
+
+    ```ruby
+    prefix(:service) do
+      config.x.service.api_key    = env(:api_key)    # Looks up "SERVICE_API_KEY"
+      config.x.service.api_secret = env(:api_secret) # Looks up "SERVICE_API_SECRET"
+    end
+    ```
+
+    Note that left hand side is unaffected. Only loadout helpers get auto-prefixed.
+
+14. If you'd like a way to shorten the left hand side too, you can assign the whole group as a hash or OrderedOptions (this is not a loadout feature, just something you can do with Rails):
+
+    ```ruby
+    prefix(:service) do
+      config.x.service = ActiveSupport::OrderedOptions[
+        api_key:    env(:api_key),
+        api_secret: env(:api_secret)
+      ]
+    end
+    ```
+
+15. Since `prefix` returns the block's result, you can rewrite the above as follows: 
+
+    ```ruby
+    config.x.service = prefix(:service) {
+      ActiveSupport::OrderedOptions[
+        api_key:    env(:api_key),
+        api_secret: env(:api_secret)
+      ]
+    }
+    ```
+
+16. `prefix` lets you supply a default to the whole block:
+
+    ```ruby
+    prefix(:service, default: -> { 'SECRET' }) do
+      config.x.service.api_key    = env(:api_key)    # falls back to 'SECRET'
+      config.x.service.api_secret = env(:api_secret) # falls back to 'SECRET'
+    end
+    ```
+
+## Advanced configuration
+
+### I don't like all these helpers polluting my config!
+
+Instead of `extend Loadout::Helpers` you can `extend Loadout` to include one proxy method `loadout`. Now all helpers live in one place.
+
+```ruby
+Rails.application.configure do
+  extend Loadout
+
+  config.some_key = loadout.cred.env(:some_key)
+end
+```
+
+Feel free to alias it to something shorter if you'd like:
+
+```ruby
+Rails.application.configure do
+  extend Loadout
+  alias l loadout
+
+  config.some_key = l.cred.env(:some_key)
+end
+```
+
+### Credentials and ENV
+
+By default loadout will look into `credentials` and `ENV` in your config's context. If your credentials are called something else, or you want to supply an alternative source of ENV, you can configure it like so:
+
+```ruby
+Rails.application.configure do
+  extend Loadout::Helpers
+  loadout creds: alt_credentials, env: alt_env
+
+  # Now loadout will use alt_credentials and alt_env to look up values.
+end
+```
+
+
+## Development
+
+After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake test` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.
+
+To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and the created tag, and push the `.gem` file to [rubygems.org](https://rubygems.org).
+
+## Contributing
+
+Bug reports and pull requests are welcome on GitHub at https://github.com/[USERNAME]/loadout. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the [code of conduct](https://github.com/[USERNAME]/loadout/blob/main/CODE_OF_CONDUCT.md).
+
+## License
+
+The gem is available as open source under the terms of the [MIT License](https://opensource.org/licenses/MIT).
+
+## Code of Conduct
+
+Everyone interacting in the Loadout project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the [code of conduct](https://github.com/[USERNAME]/loadout/blob/main/CODE_OF_CONDUCT.md).
diff --git a/Rakefile b/Rakefile
new file mode 100644
index 0000000..6983b59
--- /dev/null
+++ b/Rakefile
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+require 'bundler/gem_tasks'
+require 'minitest/test_task'
+
+Minitest::TestTask.create
+
+task default: :test
diff --git a/bin/console b/bin/console
new file mode 100755
index 0000000..9dcee67
--- /dev/null
+++ b/bin/console
@@ -0,0 +1,16 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+require 'bundler/setup'
+require 'loadout'
+require 'irb'
+
+config = Class.new.new.tap { _1.extend(Loadout::Helpers) }
+
+config.instance_eval do
+  loadout(env: $env = { 'VAR' => 'var' }, creds: $cred = { cred: 'cred' })
+
+  # You're inside the config. Call cred, env, or any other loadout helpers.
+  # Override $env or $cred to test different configurations.
+  binding.irb
+end
diff --git a/bin/setup b/bin/setup
new file mode 100755
index 0000000..cf4ad25
--- /dev/null
+++ b/bin/setup
@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+set -euo pipefail
+IFS=$'\n\t'
+set -vx
+
+bundle install
diff --git a/lib/loadout.rb b/lib/loadout.rb
new file mode 100644
index 0000000..5374944
--- /dev/null
+++ b/lib/loadout.rb
@@ -0,0 +1,160 @@
+# frozen_string_literal: true
+
+require_relative 'loadout/version'
+
+module Loadout
+  NONE = BasicObject.new
+  DEFAULT_LIST_SEP = /\s*[\s[[:punct:]]]+\s*/
+
+  ConfigError = Class.new(ArgumentError)
+  MissingConfigError = Class.new(ConfigError)
+  InvalidConfigError = Class.new(ConfigError)
+
+  def loadout(env: nil, creds: nil)
+    @loadout ||= Loadout::Config.new(env || ENV, creds || credentials)
+  end
+
+  module Helpers
+    def loadout(env: nil, creds: nil)
+      @loadout ||= Loadout::Config.new(env || ENV, creds || credentials)
+    end
+
+    def cred(*, **, &)   = loadout.cred(*, **, &)
+    def env(*, **, &)    = loadout.env(*, **, &)
+    def prefix(*, **, &) = loadout.prefix(*, **, &)
+
+    def bool(*, **, &)  = loadout.bool(*, **, &)
+    def int(*, **, &)   = loadout.int(*, **, &)
+    def float(*, **, &) = loadout.float(*, **, &)
+    def list(*, **, &)  = loadout.list(*, **, &)
+  end
+
+  class Config
+    protected attr_writer :type
+    protected attr_reader :lookup_stack
+
+    def initialize(env, creds)
+      @env = env
+      @creds = creds
+      @type = nil
+      @prefix_stack = []
+      @lookup_stack = Set[]
+      @prefix_default = NONE
+    end
+
+    def env(*keys, &default)
+      return dup.tap { _1.lookup_stack << :env } if keys.empty?
+      @lookup_stack << :env
+      lookup(keys, &default)
+    end
+
+    def cred(*keys, &default)
+      return dup.tap { _1.lookup_stack << :cred } if keys.empty?
+      @lookup_stack << :cred
+      lookup(keys, &default)
+    end
+
+    def prefix(*keys, default: NONE)
+      @prefix_default = default unless default.equal?(NONE)
+      @prefix_stack.push(keys)
+      yield.tap { @prefix_stack.pop }
+    end
+
+    def bool                         = dup.tap { _1.type = :bool }
+    def int                          = dup.tap { _1.type = :int }
+    def float                        = dup.tap { _1.type = :float }
+    def list(sep = DEFAULT_LIST_SEP) = dup.tap { _1.type = [:list, sep] }
+
+    def initialize_dup(other)
+      @creds          = other.instance_variable_get(:@creds)
+      @type           = other.instance_variable_get(:@type).dup
+      @prefix_stack   = other.instance_variable_get(:@prefix_stack).dup
+      @lookup_stack   = other.instance_variable_get(:@lookup_stack).dup
+
+      unless other.instance_variable_get(:@prefix_default).equal?(NONE)
+        @prefix_default = other.instance_variable_get(:@prefix_default).dup
+      end
+
+      super
+    end
+
+    private
+
+    def lookup(keys)
+      value = NONE
+      keys = @prefix_stack.flatten + keys
+
+      @lookup_stack.each do |source|
+        value =
+          case source
+          when :cred; lookup_cred(keys)
+          when :env;  lookup_env(keys)
+          end
+
+        return value unless value.equal?(NONE)
+      end
+
+      return yield if block_given?
+      return @prefix_default.call unless @prefix_default.equal?(NONE)
+      raise_missing(keys)
+    ensure
+      @lookup_stack.clear
+    end
+
+    def lookup_cred(keys)
+      return @creds[keys[0]] if keys.one? && @creds.has_key?(keys[0])
+      return NONE if keys.one?
+      hash = @creds.dig(*keys[..-2])
+      hash&.has_key?(keys.last) ? hash[keys.last] : NONE
+    end
+
+    def lookup_env(keys)
+      env_key = keys.join('_').upcase
+      @env.has_key?(env_key) ? coerce(env_key, @env[env_key]) : NONE
+    end
+
+    def coerce(key, value)
+      case @type
+      in :bool
+        value = value.to_s
+        return false if value == ''
+        return false if %w[0 n no f false].include?(value.downcase)
+        return true  if %w[1 y yes t true].include?(value.downcase)
+        raise_invalid :bool, key, value
+      in :int; enhance_exception(:int, key, value) { Integer(value) }
+      in :float; enhance_exception(:float, key, value) { Float(value) }
+      in :list, sep; value.split(sep)
+      else; value
+      end
+    end
+
+    def enhance_exception(type, key, val)
+      yield
+    rescue ArgumentError
+      raise_invalid(type, key, val)
+    end
+
+    def raise_missing(keys)
+      src = []
+      val = []
+
+      @lookup_stack.each do |source|
+        case source
+        when :cred
+          src << "credential"
+          val << keys.join('.')
+        when :env
+          src << "environment variable"
+          val << keys.join('_').upcase
+        end
+      end
+
+      msg = src.zip(val).map { |s, v| "#{s} (#{v})" }.join(' or ')
+      raise MissingConfigError, "required #{msg} is not set"
+    end
+
+    def raise_invalid(type, key, val)
+      raise InvalidConfigError, "invalid value for #{type} (`#{val}`) in #{key}"
+    end
+  end
+end
diff --git a/lib/loadout/version.rb b/lib/loadout/version.rb
new file mode 100644
index 0000000..5c849f3
--- /dev/null
+++ b/lib/loadout/version.rb
@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+module Loadout
+  VERSION = '0.1.0'
+end
diff --git a/loadout.gemspec b/loadout.gemspec
new file mode 100644
index 0000000..b1dc311
--- /dev/null
+++ b/loadout.gemspec
@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+require_relative 'lib/loadout/version'
+
+Gem::Specification.new do |spec|
+  spec.name = 'loadout'
+  spec.version = Loadout::VERSION
+  spec.authors = ['Max Chernyak']
+  spec.email = ['hello@max.engineer']
+
+  spec.summary = 'Rails configuration helpers'
+  spec.description = 'A few helpers to make vanilla Rails configuration neater.'
+  spec.homepage = 'https://github.com/maxim/loadout'
+  spec.license = 'MIT'
+  spec.required_ruby_version = '>= 3.0.0'
+
+  spec.metadata['allowed_push_host'] = 'https://rubygems.org'
+
+  spec.metadata['homepage_uri'] = spec.homepage
+  spec.metadata['source_code_uri'] = spec.homepage
+  spec.metadata['changelog_uri'] = "#{spec.homepage}/blob/main/CHANGELOG.md"
+
+  # Specify which files should be added to the gem when it is released.
+  # The `git ls-files -z` loads the files in the RubyGem that have been added into git.
+  gemspec = File.basename(__FILE__)
+  spec.files = IO.popen(%w[git ls-files -z], chdir: __dir__, err: IO::NULL) do |ls|
+    ls.readlines("\x0", chomp: true).reject do |f|
+      (f == gemspec) || f.start_with?(*%w[bin/ test/ .git .github Gemfile])
+    end
+  end
+  spec.bindir = 'exe'
+  spec.executables = spec.files.grep(%r{\Aexe/}) { |f| File.basename(f) }
+  spec.require_paths = ['lib']
+end
diff --git a/test/test_helper.rb b/test/test_helper.rb
new file mode 100644
index 0000000..541c36a
--- /dev/null
+++ b/test/test_helper.rb
@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+$LOAD_PATH.unshift File.expand_path('../lib', __dir__)
+require 'loadout'
+require 'minitest/autorun'
diff --git a/test/test_loadout.rb b/test/test_loadout.rb
new file mode 100644
index 0000000..086cb5e
--- /dev/null
+++ b/test/test_loadout.rb
@@ -0,0 +1,602 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class TestLoadout < Minitest::Test
+  ENV_KEY = 'LOADOUT_TEST_ENV'
+  ENV_SYM = ENV_KEY.downcase.to_sym
+  ENV_SYMS = ENV_KEY.split('_').map { _1.downcase.to_sym }
+
+  def setup
+    config_class = Class.new { attr_accessor :credentials }
+
+    @config1 = config_class.new.tap { _1.extend(Loadout) }
+    @config1.credentials = {}
+
+    @config2 = config_class.new.tap { _1.extend(Loadout::Helpers) }
+    @config2.credentials = {}
+  end
+
+  def teardown = ENV.delete(ENV_KEY)
+
+  ##############################################################################
+  # MODULE INCLUDE TESTS                                                       #
+  ##############################################################################
+  def test_config_without_helpers_has_only_loadout
+    assert_respond_to @config1, :loadout
+
+    refute_respond_to @config1, :cred
+    refute_respond_to @config1, :env
+    refute_respond_to @config1, :prefix
+    refute_respond_to @config1, :bool
+    refute_respond_to @config1, :int
+    refute_respond_to @config1, :float
+    refute_respond_to @config1, :list
+  end
+
+  def test_config_with_helpers_has_all_helpers
+    assert_respond_to @config2, :loadout
+    assert_respond_to @config2, :cred
+    assert_respond_to @config2, :env
+    assert_respond_to @config2, :prefix
+    assert_respond_to @config2, :bool
+    assert_respond_to @config2, :int
+    assert_respond_to @config2, :float
+    assert_respond_to @config2, :list
+  end
+
+  def test_env_and_creds_are_configurable
+    alt_env = { 'FOO' => 'bar' }
+    alt_creds = { baz: 'qux' }
+    c1 = Class.new.new.tap { _1.extend(Loadout) }
+    c2 = Class.new.new.tap { _1.extend(Loadout::Helpers) }
+
+    c1.loadout(creds: alt_creds, env: alt_env)
+    assert_equal 'bar', c1.loadout.env(:foo)
+    assert_equal 'qux', c1.loadout.cred(:baz)
+    assert_equal ['bar'], c1.loadout.list.env(:foo)
+    assert_equal 'qux', c1.loadout.list.env.cred(:baz)
+
+    c2.loadout(creds: alt_creds, env: alt_env)
+    assert_equal 'bar', c2.env(:foo)
+    assert_equal 'qux', c2.cred(:baz)
+    assert_equal ['bar'], c2.list.env(:foo)
+    assert_equal 'qux', c2.list.list.env.cred(:baz)
+  end
+
+  def test_loadout_can_be_aliased
+    @config1.instance_eval { alias l loadout }
+    set_env 'foo'
+    assert_equal 'foo', @config1.l.env(ENV_SYM)
+  end
+
+  ##############################################################################
+  # CRED, ENV, PREFIX ISOLATION TESTS                                          #
+  ##############################################################################
+  def test_cred_looks_up_cred_over_default
+    @config1.credentials = { foo: 'cred', bar: { baz: 'cred2' } }
+    @config2.credentials = { foo: 'cred', bar: { baz: 'cred2' } }
+
+    assert_equal 'cred', @config1.loadout.cred(:foo) { 'default' }
+    assert_equal 'cred', @config2.loadout.cred(:foo) { 'default' }
+    assert_equal 'cred', @config2.cred(:foo) { 'default' }
+
+    assert_equal 'cred2', @config1.loadout.cred(:bar, :baz) { 'default' }
+    assert_equal 'cred2', @config2.loadout.cred(:bar, :baz) { 'default' }
+    assert_equal 'cred2', @config2.cred(:bar, :baz) { 'default' }
+  end
+
+  def test_cred_looks_up_default_when_cred_is_missing
+    assert_equal 'default', @config1.loadout.cred(:foo) { 'default' }
+    assert_equal 'default', @config1.loadout.cred(:bar, :baz) { 'default' }
+    assert_equal 'default', @config2.cred(:foo) { 'default' }
+    assert_equal 'default', @config2.cred(:bar, :baz) { 'default' }
+  end
+
+  def test_cred_raises_when_cred_and_default_are_missing
+    ex = assert_raises(Loadout::MissingConfigError) {
+      @config1.loadout.cred(:a, :b)
+    }
+    assert_equal 'required credential (a.b) is not set', ex.message
+
+    ex = assert_raises(Loadout::MissingConfigError) { @config2.cred(:a, :b) }
+    assert_equal 'required credential (a.b) is not set', ex.message
+  end
+
+  def test_env_looks_up_env_over_default
+    set_env 'env'
+    assert_equal 'env', @config1.loadout.env(:loadout_test_env) { 'default' }
+    assert_equal 'env', @config2.loadout.env(:loadout_test_env) { 'default' }
+    assert_equal 'env', @config2.env(:loadout_test_env) { 'default' }
+  end
+
+  def test_env_looks_up_default_when_env_is_missing
+    assert_equal 'default', @config1.loadout.env(:foo) { 'default' }
+    assert_equal 'default', @config2.env(:foo) { 'default'}
+  end
+
+  def test_env_raises_when_env_and_default_are_missing
+    ex = assert_raises(Loadout::ConfigError) { @config1.loadout.env(*ENV_SYMS) }
+    assert_equal "required environment variable (#{ENV_KEY}) is not set",
+      ex.message
+
+    ex = assert_raises(Loadout::ConfigError) { @config2.env(*ENV_SYMS) }
+    assert_equal "required environment variable (#{ENV_KEY}) is not set",
+      ex.message
+  end
+
+  def test_prefix_looks_up_nested_cred
+    @config1.credentials = { foo: { bar: { baz: 'cred' } } }
+    @config2.credentials = { foo: { bar: { baz: 'cred' } } }
+
+    value1 = @config1.instance_eval {
+      loadout.prefix(:foo) { loadout.prefix(:bar) { loadout.cred(:baz) } }
+    }
+
+    value2 = @config2.instance_eval {
+      prefix(:foo) { prefix(:bar) { cred(:baz) } }
+    }
+
+    assert_equal 'cred', value1
+    assert_equal 'cred', value2
+  end
+
+  def test_prefix_applies_default_to_nested_cred
+    value1 = @config1.instance_eval {
+      loadout.prefix(:foo, default: -> { 'default' }) {
+        loadout.prefix(:bar) {
+          loadout.cred(:baz)
+        }
+      }
+    }
+
+    value2 = @config2.instance_eval {
+      prefix(:foo) {
+        prefix(:bar, default: -> { 'default' }) {
+          cred(:baz)
+        }
+      }
+    }
+
+    assert_equal 'default', value1
+    assert_equal 'default', value2
+  end
+
+  def test_prefix_shows_key_in_cred_error
+    ex = assert_raises(Loadout::ConfigError) {
+      @config1.instance_eval { loadout.prefix(:foo) { loadout.cred(:bar) } }
+    }
+
+    assert_equal 'required credential (foo.bar) is not set', ex.message
+
+    ex = assert_raises(Loadout::ConfigError) {
+      @config2.instance_eval { prefix(:foo) { cred(:bar) } }
+    }
+
+    assert_equal 'required credential (foo.bar) is not set', ex.message
+  end
+
+  def test_prefix_looks_up_nested_env
+    set_env 'env'
+
+    value1 = @config1.instance_eval {
+      loadout.prefix(:loadout) { loadout.prefix(:test) { loadout.env(:env) } }
+    }
+
+    value2 = @config2.instance_eval {
+      prefix(:loadout) { prefix(:test) { env(:env) } }
+    }
+
+    assert_equal 'env', value1
+    assert_equal 'env', value2
+  end
+
+  def test_prefix_applies_default_to_nested_env
+    value1 = @config1.instance_eval {
+      loadout.prefix(:foo, default: -> { 'default' }) {
+        loadout.prefix(:bar) {
+          loadout.env(:baz)
+        }
+      }
+    }
+
+    value2 = @config2.instance_eval {
+      prefix(:foo) {
+        prefix(:bar, default: -> { 'default' }) {
+          env(:baz)
+        }
+      }
+    }
+
+    assert_equal 'default', value1
+    assert_equal 'default', value2
+  end
+
+  def test_prefix_shows_key_in_env_error
+    ex = assert_raises(Loadout::ConfigError) {
+      @config1.instance_eval { loadout.prefix(:loadout) { loadout.env(:test) } }
+    }
+
+    assert_equal 'required environment variable (LOADOUT_TEST) is not set',
+      ex.message
+
+    ex = assert_raises(Loadout::ConfigError) {
+      @config2.instance_eval { prefix(:loadout) { env(:test) } }
+    }
+
+    assert_equal 'required environment variable (LOADOUT_TEST) is not set',
+      ex.message
+  end
+
+  ##############################################################################
+  # BOOL TESTS                                                                 #
+  ##############################################################################
+  def test_bool_accepts_falsy_strings
+    ['', 'false', 'F', 'nO', 'n', '0'].each do |value|
+      set_env value
+      assert_equal false, @config1.loadout.bool.env(ENV_SYM)
+      assert_equal false, @config2.loadout.bool.env(ENV_SYM)
+      assert_equal false, @config2.bool.env(ENV_SYM)
+    end
+  end
+
+  def test_bool_accepts_truthy_strings
+    ['1', 'true', 't', 'yes', 'Y'].each do |value|
+      set_env value
+      assert_equal true, @config1.loadout.bool.env(ENV_SYM)
+      assert_equal true, @config2.loadout.bool.env(ENV_SYM)
+      assert_equal true, @config2.bool.env(ENV_SYM)
+    end
+  end
+
+  def test_bool_raises_on_missing_key
+    ex = assert_raises(Loadout::ConfigError) {
+      @config1.loadout.bool.env(ENV_SYM)
+    }
+
+    assert_equal "required environment variable (#{ENV_KEY}) is not set",
+      ex.message
+
+    ex = assert_raises(Loadout::ConfigError) { @config2.bool.env(ENV_SYM) }
+    assert_equal "required environment variable (#{ENV_KEY}) is not set",
+      ex.message
+  end
+
+  def test_bool_raises_on_invalid_string
+    ['bad', 'tr', '#'].each do |value|
+      set_env value
+
+      ex = assert_raises(Loadout::ConfigError) {
+        @config1.loadout.bool.env(ENV_SYM)
+      }
+
+      assert_equal "invalid value for bool (`#{value}`) in #{ENV_KEY}",
+        ex.message
+
+      ex = assert_raises(Loadout::ConfigError) { @config2.bool.env(ENV_SYM) }
+      assert_equal "invalid value for bool (`#{value}`) in #{ENV_KEY}",
+        ex.message
+    end
+  end
+
+  def test_bool_does_not_raise_with_default
+    assert_equal true, @config1.loadout.bool.env(ENV_SYM) { true }
+    assert_equal true, @config2.bool.env(ENV_SYM) { true }
+  end
+
+  def test_bool_raises_with_invalid_string_and_default
+    set_env 'bad'
+
+    ex = assert_raises(Loadout::ConfigError) {
+      @config1.loadout.bool.env(ENV_SYM) { true }
+    }
+    assert_equal "invalid value for bool (`bad`) in #{ENV_KEY}", ex.message
+
+    ex = assert_raises(Loadout::ConfigError) {
+      @config2.bool.env(ENV_SYM) { true }
+    }
+    assert_equal "invalid value for bool (`bad`) in #{ENV_KEY}", ex.message
+  end
+
+  ##############################################################################
+  # INT TESTS                                                                  #
+  ##############################################################################
+  def test_int_coerces_string_to_integer
+    set_env '42'
+    assert_equal 42, @config1.loadout.int.env(ENV_SYM)
+    assert_equal 42, @config2.loadout.int.env(ENV_SYM)
+    assert_equal 42, @config2.int.env(ENV_SYM)
+  end
+
+  def test_int_raises_on_missing_key
+    ex = assert_raises(Loadout::ConfigError) {
+      @config1.loadout.int.env(ENV_SYM)
+    }
+    assert_equal "required environment variable (#{ENV_KEY}) is not set",
+      ex.message
+
+    ex = assert_raises(Loadout::ConfigError) { @config2.int.env(ENV_SYM) }
+    assert_equal "required environment variable (#{ENV_KEY}) is not set",
+      ex.message
+  end
+
+  def test_int_raises_on_invalid_string
+    set_env 'bad'
+
+    ex = assert_raises(Loadout::ConfigError) {
+      @config1.loadout.int.env(ENV_SYM)
+    }
+    assert_equal "invalid value for int (`bad`) in #{ENV_KEY}", ex.message
+
+    ex = assert_raises(Loadout::ConfigError) { @config2.int.env(ENV_SYM) }
+    assert_equal "invalid value for int (`bad`) in #{ENV_KEY}", ex.message
+  end
+
+  def test_int_does_not_raise_with_default
+    assert_equal 42, @config1.loadout.int.env(ENV_SYM) { 42 }
+    assert_equal 42, @config2.int.env(ENV_SYM) { 42 }
+  end
+
+  def test_int_raises_with_invalid_string_and_default
+    set_env 'bad'
+
+    ex = assert_raises(Loadout::ConfigError) {
+      @config1.loadout.int.env(ENV_SYM) { 42 }
+    }
+    assert_equal "invalid value for int (`bad`) in #{ENV_KEY}", ex.message
+
+    ex = assert_raises(Loadout::ConfigError) { @config2.int.env(ENV_SYM) { 42 } }
+    assert_equal "invalid value for int (`bad`) in #{ENV_KEY}", ex.message
+  end
+
+  ##############################################################################
+  # FLOAT TESTS                                                                #
+  ##############################################################################
+  def test_float_coerces_string_to_float
+    set_env '3.14'
+    assert_equal 3.14, @config1.loadout.float.env(ENV_SYM)
+    assert_equal 3.14, @config2.loadout.float.env(ENV_SYM)
+    assert_equal 3.14, @config2.float.env(ENV_SYM)
+  end
+
+  def test_float_raises_on_missing_key
+    ex = assert_raises(Loadout::ConfigError) {
+      @config1.loadout.float.env(ENV_SYM)
+    }
+    assert_equal "required environment variable (#{ENV_KEY}) is not set",
+      ex.message
+
+    ex = assert_raises(Loadout::ConfigError) { @config2.float.env(ENV_SYM) }
+    assert_equal "required environment variable (#{ENV_KEY}) is not set",
+      ex.message
+  end
+
+  def test_float_raises_on_invalid_string
+    set_env 'bad'
+
+    ex = assert_raises(Loadout::ConfigError) {
+      @config1.loadout.float.env(ENV_SYM)
+    }
+    assert_equal "invalid value for float (`bad`) in #{ENV_KEY}", ex.message
+
+    ex = assert_raises(Loadout::ConfigError) { @config2.float.env(ENV_SYM) }
+    assert_equal "invalid value for float (`bad`) in #{ENV_KEY}", ex.message
+  end
+
+  def test_float_does_not_raise_with_default
+    assert_equal 3.14, @config1.loadout.float.env(ENV_SYM) { 3.14 }
+    assert_equal 3.14, @config2.float.env(ENV_SYM) { 3.14 }
+  end
+
+  def test_float_raises_with_invalid_string_and_default
+    set_env 'bad'
+
+    ex = assert_raises(Loadout::ConfigError) {
+      @config1.loadout.float.env(ENV_SYM) { 3.14 }
+    }
+    assert_equal "invalid value for float (`bad`) in #{ENV_KEY}", ex.message
+
+    ex = assert_raises(Loadout::ConfigError) { @config2.float.env(ENV_SYM) { 3.14 } }
+    assert_equal "invalid value for float (`bad`) in #{ENV_KEY}", ex.message
+  end
+
+  ##############################################################################
+  # LIST TESTS                                                                 #
+  ##############################################################################
+  def test_list_splits_string_by_various_separators
+    set_env 'a,b, c'
+    assert_equal %w[a b c], @config1.loadout.list.env(ENV_SYM)
+    assert_equal %w[a b c], @config2.loadout.list.env(ENV_SYM)
+    assert_equal %w[a b c], @config2.list.env(ENV_SYM)
+
+    set_env 'a b   c'
+    assert_equal %w[a b c], @config1.loadout.list.env(ENV_SYM)
+    assert_equal %w[a b c], @config2.loadout.list.env(ENV_SYM)
+    assert_equal %w[a b c], @config2.list.env(ENV_SYM)
+
+    set_env 'a |  b:c'
+    assert_equal %w[a b c], @config1.loadout.list.env(ENV_SYM)
+    assert_equal %w[a b c], @config2.loadout.list.env(ENV_SYM)
+    assert_equal %w[a b c], @config2.list.env(ENV_SYM)
+
+    set_env '1 - 2; 3'
+    assert_equal %w[1 2 3], @config1.loadout.list.env(ENV_SYM)
+    assert_equal %w[1 2 3], @config2.loadout.list.env(ENV_SYM)
+    assert_equal %w[1 2 3], @config2.list.env(ENV_SYM)
+  end
+
+  def test_list_separator_is_configurable
+    set_env 'a |b| c'
+    assert_equal ['a ', 'b', ' c'], @config1.loadout.list('|').env(ENV_SYM)
+    assert_equal ['a ', 'b', ' c'], @config2.loadout.list('|').env(ENV_SYM)
+    assert_equal ['a ', 'b', ' c'], @config2.list('|').env(ENV_SYM)
+  end
+
+  def test_list_raises_on_missing_key
+    ex = assert_raises(Loadout::ConfigError) {
+      @config1.loadout.list.env(ENV_SYM)
+    }
+    assert_equal "required environment variable (#{ENV_KEY}) is not set",
+      ex.message
+
+    ex = assert_raises(Loadout::ConfigError) { @config2.list.env(ENV_SYM) }
+    assert_equal "required environment variable (#{ENV_KEY}) is not set",
+      ex.message
+  end
+
+  def test_list_does_not_raise_with_default
+    assert_equal %w[a b c], @config1.loadout.list.env(ENV_SYM) { %w[a b c] }
+    assert_equal %w[a b c], @config2.list.env(ENV_SYM) { %w[a b c] }
+  end
+
+  ##############################################################################
+  # COMBO TESTS                                                                #
+  ##############################################################################
+  def test_cred_env_looks_up_cred
+    @config1.credentials = { ENV_SYM => 'cred' }
+    @config2.credentials = { ENV_SYM => 'cred' }
+    set_env 'env'
+
+    assert_equal 'cred', @config1.loadout.cred.env(ENV_SYM)
+    assert_equal 'cred', @config2.loadout.cred.env(ENV_SYM)
+    assert_equal 'cred', @config2.cred.env(ENV_SYM)
+  end
+
+  def test_cred_env_looks_up_nested_cred
+    @config1.credentials = { loadout: { test: { env: 'cred' } } }
+    @config2.credentials = { loadout: { test: { env: 'cred' } } }
+
+    assert_equal 'cred', @config1.loadout.cred.env(*ENV_SYMS)
+    assert_equal 'cred', @config2.loadout.cred.env(*ENV_SYMS)
+    assert_equal 'cred', @config2.cred.env(*ENV_SYMS)
+  end
+
+  def test_cred_env_looks_up_env_after_cred
+    set_env 'env'
+
+    assert_equal 'env', @config1.loadout.cred.env(ENV_SYM) { 'default' }
+    assert_equal 'env', @config2.loadout.cred.env(ENV_SYM) { 'default' }
+    assert_equal 'env', @config2.cred.env(ENV_SYM) { 'default' }
+  end
+
+  def test_cred_env_looks_up_default_after_cred_and_env
+    assert_equal 'default', @config1.loadout.cred.env(ENV_SYM) { 'default' }
+    assert_equal 'default', @config2.loadout.cred.env(ENV_SYM) { 'default' }
+    assert_equal 'default', @config2.cred.env(ENV_SYM) { 'default' }
+  end
+
+  def test_bool_cred_env_looks_up_bool_cred
+    @config1.credentials = { ENV_SYM => true }
+    @config2.credentials = { ENV_SYM => true }
+    set_env 'false'
+
+    assert_equal true, @config1.loadout.bool.cred.env(ENV_SYM)
+    assert_equal true, @config2.loadout.bool.cred.env(ENV_SYM)
+    assert_equal true, @config2.bool.cred.env(ENV_SYM)
+  end
+
+  def test_bool_cred_env_looks_up_bool_env
+    set_env 'true'
+
+    assert_equal true, @config1.loadout.bool.cred.env(ENV_SYM) { 'default' }
+    assert_equal true, @config2.loadout.bool.cred.env(ENV_SYM) { 'default' }
+    assert_equal true, @config2.bool.cred.env(ENV_SYM) { 'default' }
+  end
+
+  def test_bool_cred_env_looks_up_bool_default
+    assert_equal false, @config1.loadout.bool.cred.env(ENV_SYM) { false }
+    assert_equal false, @config2.loadout.bool.cred.env(ENV_SYM) { false }
+    assert_equal false, @config2.bool.cred.env(ENV_SYM) { false }
+  end
+
+  def test_env_cred_looks_up_env
+    @config1.credentials = { ENV_SYM => 'cred' }
+    @config2.credentials = { ENV_SYM => 'cred' }
+    set_env 'env'
+
+    assert_equal 'env', @config1.loadout.env.cred(ENV_SYM)
+    assert_equal 'env', @config2.loadout.env.cred(ENV_SYM)
+    assert_equal 'env', @config2.env.cred(ENV_SYM)
+  end
+
+  def test_env_cred_looks_up_cred_after_env
+    set_env 'env'
+
+    assert_equal 'env', @config1.loadout.env.cred(ENV_SYM) { 'default' }
+    assert_equal 'env', @config2.loadout.env.cred(ENV_SYM) { 'default' }
+    assert_equal 'env', @config2.env.cred(ENV_SYM) { 'default' }
+  end
+
+  def test_env_cred_looks_up_default_after_env_and_cred
+    assert_equal 'default', @config1.loadout.env.cred(ENV_SYM) { 'default' }
+    assert_equal 'default', @config2.loadout.env.cred(ENV_SYM) { 'default' }
+    assert_equal 'default', @config2.env.cred(ENV_SYM) { 'default' }
+  end
+
+  def test_bool_env_cred_looks_up_bool_env
+    set_env 'true'
+
+    assert_equal true, @config1.loadout.bool.env.cred(ENV_SYM)
+    assert_equal true, @config2.loadout.bool.env.cred(ENV_SYM)
+    assert_equal true, @config2.bool.env.cred(ENV_SYM)
+  end
+
+  def test_bool_env_cred_looks_up_bool_cred
+    @config1.credentials = { ENV_SYM => true }
+    @config2.credentials = { ENV_SYM => true }
+
+    assert_equal true, @config1.loadout.bool.env.cred(ENV_SYM) { 'default' }
+    assert_equal true, @config2.loadout.bool.env.cred(ENV_SYM) { 'default' }
+    assert_equal true, @config2.bool.env.cred(ENV_SYM) { 'default' }
+  end
+
+  def test_bool_env_cred_looks_up_bool_default
+    assert_equal true, @config1.loadout.bool.env.cred(ENV_SYM) { true }
+    assert_equal true, @config2.loadout.bool.env.cred(ENV_SYM) { true }
+    assert_equal true, @config2.bool.env.cred(ENV_SYM) { true }
+  end
+
+  def test_prefix_cred_env_looks_up_nested_cred
+    @config1.credentials = { loadout: { test: { env: 'cred' } } }
+    @config2.credentials = { loadout: { test: { env: 'cred' } } }
+    set_env 'env'
+
+    value1 = @config1.instance_eval {
+      loadout.prefix(:loadout) {
+        loadout.prefix(:test) {
+          loadout.cred.env(:env)
+        }
+      }
+    }
+
+    value2 = @config2.instance_eval {
+      prefix(:loadout) { prefix(:test) { cred.env(:env) } }
+    }
+
+    assert_equal 'cred', value1
+    assert_equal 'cred', value2
+  end
+
+  def test_prefix_cred_env_looks_up_nested_env
+    set_env 'env'
+
+    value1 = @config1.instance_eval {
+      loadout.prefix(:loadout) {
+        loadout.prefix(:test) {
+          loadout.cred.env(:env)
+        }
+      }
+    }
+
+    value2 = @config2.instance_eval {
+      prefix(:loadout) { prefix(:test) { cred.env(:env) } }
+    }
+
+    assert_equal 'env', value1
+    assert_equal 'env', value2
+  end
+
+  private
+
+  def set_env(value) = ENV[ENV_KEY] = value
+end