Replaces any given exception that happens inside a block with a new one. @garybernhardt "if this call raises exception Foo, I want you to raise exception Bar".

replace_exception.rb

def replace_exception original_exception, new_exception
  begin
    yield
  rescue original_exception
    raise new_exception
  end
end

class OtherException < Exception; end
class UselessException < Exception; end
class SomeException < Exception; end

describe 'Replace exception' do
  context 'When the original exception is raised' do
    it 'Raises the new exception' do
      lambda do
        replace_exception SomeException, OtherException do
          raise SomeException
        end
      end.should raise_error OtherException
    end
  end

  context 'When no exception is raised' do
    it 'Does not raise exception' do
      lambda do
        replace_exception SomeException, OtherException do
        end
      end.should_not raise_error
    end
  end

  context 'When the original exception is not raised' do
    it 'Does not raise the new exception' do
      lambda do
        replace_exception SomeException, OtherException do
          raise UselessException
        end
      end.should raise_error UselessException
    end
  end
end