Silencing Deprecation Warnings in Rspec

Published 11 January 11 by Justin French

If you’re testing the behavior of deprecated code in your Ruby project, the warning messages littered throughout your spec output is incredibly noisy.

You could silence all warnings with ::ActiveSupport::Deprecation.silenced = true, but you might miss out on an important warning in one of your dependencies. It’s tempting to remove the tests altogether (the code will be burned soon too, right?), but I figured out something a little nicer a little while back in Formtastic’s test suite.

Throw this code in spec/support/deprecations.rb:

def with_deprecation_silenced(&block)
  previous_setting = ::ActiveSupport::Deprecation.silenced
  ::ActiveSupport::Deprecation.silenced = true
  yield
  ::ActiveSupport::Deprecation.silenced = previous_setting
end

You can then wrap that block around almost any part of your test suite to temporarily turn off the deprecation warnings. Here’s an example:

describe '#bah' do
  with_deprecation_silenced do
    it 'should be deprecated' do
      ::ActiveSupport::Deprecation.should_receive(:warn).any_number_of_times
      Foo.new.bah
    end
    it 'should return true' do
      Foo.new.bah.should be_true
    end
  end
end

Better still, I recently discovered that ActiveSupport already has method for this, but it’s currently hidden in the Rails documentation (it’ll be fixed in next stable release). So I can change my code to something like this:

def with_deprecation_silenced(&block)
  ::ActiveSupport::Deprecation.silence do
    yield
  end
end

Alternatively, we could just use the ActiveSupport method directly in our tests:

describe '#bah' do
  ::ActiveSupport::Deprecation.silence do
    it 'should be deprecated' do
      ::ActiveSupport::Deprecation.should_receive(:warn).any_number_of_times
      Foo.new.bah
    end
    it 'should return true' do
      Foo.new.bah.should be_true
    end
  end
end

The (lesser) alternative would be to roll your own in RSpec’s before and after blocks:

describe '#bah' do 
  before do
    @old_silence_config = ::ActiveSupport::Deprecation.silenced
    ::ActiveSupport::Deprecation.silenced = true
  end
  #...
  after do
    ::ActiveSupport::Deprecation.silenced = @old_silence_config
  end
end

This is one of the many simple reasons why I love Ruby’s blocks!