error matcher

error-matcher.js

var hamjest = require('hamjest')
  , util = require('util')
  , _ = require('lodash')

module.exports = error

function IsError(type, message) {
  var prop = hamjest.hasProperty('message', message)

  return _.create(new hamjest.TypeSafeMatcher(),
    { isExpectedType: function (actual) {
        return actual instanceof Error &&
          actual instanceof type
      }

    , matchesSafely: function (actual) {
        return prop.matches(actual)
      }

    , describeMismatchSafely: function (actual, description) {
        prop.describeMismatch(actual, description)
      }

    , describeTo: function (description) {
        description.append('an error with a message that is ')
        message.describeTo(description)
      }
    }
  )
}


function error(type, message) {
  if (util.isRegExp(message)) {
    message = hamjest.matchesPattern(message)
  }
  return new IsError(type, message)
}