Stubbing a block in rspec

There're at least two ways to stub a block in rspec, the first version is using `and_yield`

```ruby
config = double('Config', enabled: true)
allow(app).to receive(:config).and_yield(config)
app.config do |config|
  expect(config.enabled).to be_truthy
end
```
The second version is receiving the block

```ruby
config = double('Config', enabled: true)
allow(app).to receive(:config) do |_, &block|
  block.call(config)
end|
app.config do |config|
  expect(config.enabled).to be_truthy
end
```


Edwin Cruz
February 10, 2021