Rake tasks may take their argument values from ENV if they're not supplied

about_rake_tasks_arguments_and_env_spec.rb

require 'rake'
require 'spec'

describe 'About rake tasks, arguments and ENV' do
	before(:each) do
		ENV.delete('any_environment_variable')
		Rake::Task.clear
	end

	it 'Argument may be satisfied from the ENV array if there is none explicitly supplied when invoked' do
		the_argument_supplied = nil

		task :an_example_with_an_argument, :any_environment_variable do |_, args|
			the_argument_supplied = args.any_environment_variable
		end

		ENV['any_environment_variable'] = 'Chubby Rain and Phil Murphy\'s bike seat'
		Rake::Task[:an_example_with_an_argument].execute

		the_argument_supplied.should === 'Chubby Rain and Phil Murphy\'s bike seat'
	end

	it 'Argument is nil when there is no matching environment variable and no value supplied when invoked' do
		the_argument_supplied = nil

		task :an_example_with_an_argument, :any_environment_variable do |_, args|
			the_argument_supplied = args.any_environment_variable
		end

		Rake::Task[:an_example_with_an_argument].execute

		the_argument_supplied.should be_nil
	end

	it 'Argument may be supplied as follows' do
		the_argument_supplied = nil
		
		task :an_example_with_an_argument, :any_environment_variable do |_, args|
			the_argument_supplied = args.any_environment_variable
		end

		Rake::Task[:an_example_with_an_argument].invoke('xxx')

		the_argument_supplied.should === 'xxx'
	end

	it 'When satisfied from ENV, the key may be uppercase' do
		the_argument_supplied = nil

		task :an_example_with_an_argument, :any_environment_variable do |_, args|
			the_argument_supplied = args.any_environment_variable
		end

		ENV['ANY_ENVIRONMENT_VARIABLE'] = 'Chubby Rain and Phil Murphy\'s bike seat'
		Rake::Task[:an_example_with_an_argument].execute

		the_argument_supplied.should === 'Chubby Rain and Phil Murphy\'s bike seat'
	end

	it 'Argument overrides anything in ENV' do
		the_argument_supplied = nil

		task :an_example_with_an_argument, :any_environment_variable do |_, args|
			the_argument_supplied = args.any_environment_variable
		end

		ENV['any_environment_variable'] = 'Chubby Rain and Phil Murphy\'s bike seat'
		Rake::Task[:an_example_with_an_argument].invoke("Another kebab on a weekday")

		the_argument_supplied.should === 'Another kebab on a weekday'
	end
end

See: TaskArguments#lookup