common: add assert() function

[josephjclark]

Assert should take some expression or function and throw an error if either resolves to false.

This allows us to abort execution in the event of a fail state. It's a good replacement for eg salesforce's failOnError, and can be applied equally to all jobs and adaptors. It doesn't need special API support. Although the operation in question does need to provide enough feedback to make a useful assertion on - ie, it must write something useful to state.data.

It should take a second argument as an error message which will be returned.

Eg

assert($.data.errors === 0, "Errors detected in upsert")
assert($.data.length, "No patient data found!")

[josephjclark]

This would replace failOnError in salesforce, which is a popular pattern.

One consideration is that assert is a bit less elegant when combined with each (although you can still do it!)

each($.data, bulk(...).then(assert($.res, 'some error')))

This will run the assertion after each bulk request and throw to abort the job as soon as one fails