RSpec common practice and technique

rspec_common_practice

#stub chain of methods
```
  describe '#chain stub' do
    subject { Object.new }
    let(:stb) { double sync:calc }
    before { allow(subject).to receive_message_chain('method1.mathod2.calc') { stb } }
    before { subject.method1.mathod2.calc }
    it { expect(stb).to have_received(:calc) }
  end
```
#stub method 
```
  describe '#method stub' do
    subject { Object.new }
    let(:stb) { double sync:calc }
    before { allow(subject).to receive :method1 }
    before { subject.method1 }
    it { expect(stb).to have_received(:method1) }
  end
```
#stub method with argument check
```
  is_expected.to have_received(:update).with(array_including([ad1, ad2]))
  is_expected.to have_received(:update) { |arr| expect(arr.count).to eq 2 }
```

#count receiving messages
```
expect(...).to receive(...).once
expect(...).to receive(...).twice
expect(...).to receive(...).exactly(n).times
expect(...).to receive(...).at_least(:once)
expect(...).to receive(...).at_least(:twice)
expect(...).to receive(...).at_least(n).times
expect(...).to receive(...).at_most(:once)
expect(...).to receive(...).at_most(:twice)
expect(...).to receive(...).at_most(n).times
```