assertions

loads of useful assert functions in one package

npm install assertions
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Assertions

assertions is a powerful assertion toolkit.

there are many useful assertion functions,
including a few very useful higher order assertion functions.
also, every function has a _curry form and these can be joined together to create reusable specs.

here I'll explain:

assert that bar equals foo

var a = require('assertions')

a.equal(bar, foo)

create an assertion that anything equals foo

var equalFoo = a._equal(foo)

//apply it to some things...
equalFoo (bar)
equalFoo (baz)
equalFoo (zuk)

every function has a curry form with a leading "_",
it skips the first arg,
and returns an assertion function that you can pass the first arg to later!

okay, so why?

this starts to get super awesome when you have, example, the has assertion:

//assert that bar has a property letters: 3, and a name, which is a string.
a.has(bar, {
  letters: 3,
, name: function (actual) { a.isString(actual, 'make it a string!') }
})

has is kinda like deepEqual but only checks that the property matches if it's a primitive.
if the property is a function then has assumes that it is an assertion function,
and applys the function to the corisponding property on the actual object.

lets rewrite the above example using the curry form:

//assert that bar has a property letters: 3, and a name, which is a string.
var validTLA = a._has({
  letters: 3,
  name: a._isString('make it a string!')
}, 'must be a real Three Letter Acronym')

now we can check that every thing is a valid TLA, oh yeah, lets use the higher order assertion every

a.every([
  {name: 'WTF', letters: 3},
  {name: 'OMG', letters: 3},
  {name: 'BBQ', letters: 3},
  {name: 'TLA', letters: 3},
  {name: 'DSL', letters: 3}
], validTLA)

we can now use validTLA where ever we need to check that something is a TLA, not just in our tests.

Error Messages

one of the best things about assertions is that it creates very detailed error messages.

a.every([
  {name: 'WTF', letters: 3},
  {name: 'TLA', letters: 3},
  {name: 'IMHO', letters: 4}
  ], validTLA)

will give you a message like this, showing each step of where it went wrong!

equal: 4 == 3
has: ({ name: "IMHO", letters: 4 }).letters must match { letters: 3, name: isString }).letters
every: every[2] (== { name: "IMHO", letters: 4 }) must pass has, 
  (2 out of 3 have passed)
    at Object.equal (/home/dominic/source/dev/assertions/elementary.js:11:18)
    at Object.leaf (/home/dominic/source/dev/assertions/higher.js:175:16)
    ...

assertion(actual [, expected...], message)

that is the raw form of all assertions. this convention is borrowed from the nodejs assert module.

some times expected is not necessary, or is optional, or may take multiple args. see assertion docs.

if the assertion takes optional args, the last arg is always message if it is a string.

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