Rspec on lib + initializer

Question

I'm trying to test a lib I've created. It auto load with an initializer.

Here is what I have

# config/initializer/my_lib.rb
MyLib.configure do |config|
  config.salt   = Rails.application.secrets.encrypted_salt
  config.secret = Rails.application.secrets.encrypted_secret
end

# lib/my_lib.rb
class MyLib

  class << self
    attr_accessor :configuration

    def config
      @configuration ||= Configuration.new
    end

    def configure
      yield(config)
      raise 'Salt not specified' unless config.salt
      raise 'Secret not specified' unless config.secret
    end
  end

  class Configuration
    attr_accessor :salt, :secret
  end
end

What I would like is to test that without salt and secret, MyLib.configure will raise an RuntimeError.

I've tried the following test but I'm stuck with the block I think

allow(described_class).to receive(:configure) do |&config|
  config.salt = nil
  config.secret = nil
end

In the previous example both |config| and |&config| give me a nil value for config.

Answer 1

Use expect error:

expect do
  MyLib.configure do |config|
    config.salt   = nil
    config.secret = nil
  end
end.to raise_error RuntimeError 

But I would recommend that you create your own exception class such as MyLib::ConfigurationError as RuntimeError could have other causes and the test could actually pass if there is a bug in the code.