Support for Chai .not

[bergie]

The chai .not expectation would be super useful, for example:

-
  name: 'listing hashes after removing'
  assertion: 'should not return the same hash'
  inputs:
    pinlist: true
  expect:
    out:
      not:
        contain: 'Qmctf39Vj8aLdg9icf2kvVcENyuNWBwy5TGWvHX9CZ6UkG'

Use case: the "listing hashes after removing" test in https://github.com/noflo/noflo-ipfs/blob/master/spec/Pin.yaml

[jonnor]

I don't think we should attempt to chain / compose the expectations, that is kind-of a rabbithole. Very quickly one is inventing a whole programming language...

So I think we should just havenotFoo operators, for every Foo that we think make sense. In the implementation we can programatically generate them, if it makes sense.

Schema: https://github.com/flowbased/fbp-spec/blob/master/schemata/expectation.yaml
Implementation: https://github.com/flowbased/fbp-spec/blob/master/src/expectation.coffee#L12

[jonnor]

And then one should also add some testcases for the new operators in: https://github.com/flowbased/fbp-spec/blob/master/examples/predicates.yaml