While we often refer to these sorts of examples as "one-liners" (since it's intended to be used like `it { should matcher }` -- all on one line), they can be written on multiple lines:

``` ruby
specify do
  expect {
    do_something
  }.to raise_error(FooError)
end
```

It would be confusing to a user to call this "one line syntax" since it's multiple lines.  Instead, I would say:

```
VCR cannot infer a cassette name from the docstring-less example declared at path/to/spec.rb:14.
Give the example a doc string or add a `:cassette_name` option to your VCR metadata.
```