Unit Testing Ruby Blocks by Mocking with rr (was flexmock)

Question

How do I unit test the following:

  def update_config
    store = YAML::Store.new('config.yaml')
    store.transaction do
      store['A'] = 'a'
    end
  end

Here is my start:

  def test_yaml_store
    mock_store = flexmock('store')
    mock_store
      .should_receive(:transaction)
      .once
    flexmock(YAML::Store).should_receive(:new).returns(mock_store)
    update_config()
  end

How do I test what is inside the block?

UPDATED

I have converted my test to spec and switched to rr mocking framework:

describe 'update_config' do
  it 'calls transaction' do
    stub(YAML::Store).new do |store|
      mock(store).transaction
    end
    update_config
  end
end

This will test the transaction was called. How do I test inside the block: store['A'] = 'a'?

Answer 1

First, you can write this a little simpler -- your test using RR isn't a direct port of your test using FlexMock. Second, you're not testing what happens within the block at all so your test is incomplete. Try this instead:

describe '#update_config' do
  it 'makes a YAML::Store and stores A in it within a transaction' do
    mock_store = {}
    mock(mock_store).transaction.yields
    mock(YAML::Store).new { mock_store }
    update_config
    expect(mock_store['A']).to eq 'a'
  end
end

Note that since you're providing the implementation of #transaction, not merely the return value, you could have also said it this way:

describe '#update_config' do
  it 'makes a YAML::Store and stores A in it within a transaction' do
    mock_store = {}
    mock(mock_store).transaction { |&block| block.call }
    mock(YAML::Store).new { mock_store }
    update_config
    expect(mock_store['A']).to eq 'a'
  end
end

Answer 2

You want to call yields:

describe 'update_config' do
  it 'calls transaction which stores A = a' do
    stub(YAML::Store).new do |store|
      mock(store).transaction.yields
      mock(store).[]=('A', 'a')
    end
    update_config
  end
end

Check out this answer for a different approach to a related question. Hopefully the rr api documentation will improve.