must/lib/assertion_error.js

Testing and assertion library with friendly BDD syntax — awesome.must.be.true(). Many expressive matchers and is test runner and framework agnostic. Follows RFC 2119 with its use of MUST. Good and well tested stuff.

var O = require("oolong")
var FIRST_LINE = /^.*$/m
module.exports = AssertionError

/**
 * Error object thrown when an assertion fails.
 *
 * @class AssertionError
 * @constructor
 * @param message
 * @param [options]
 */
function AssertionError(msg, opts) {
  this.message = msg

  /**
   * The asserted object.
   *
   * @property actual
   */
  if (opts && "actual" in opts) this.actual = opts.actual

  /**
   * If the matcher took an argument or asserted against something (like
   * `foo.must.be.true()`), then this is the expected value.
   *
   * @property expected
   */
  if (opts && "expected" in opts) this.expected = opts.expected

  /**
   * Whether it makes sense to compare objects granularly or even show a diff
   * view of the objects involved.  
   *
   * Most matchers (e.g. [`empty`](#Must.prototype.empty) and
   * [`string`](#Must.prototype.string)) are concrete, strict and atomic and
   * don't lend themselves to be compared property by property.  Others however,
   * like [`eql`](#Must.prototype.eql), are more granular and comparing them
   * line by line helps understand how they differ.
   *
   * @property diffable
   */
  if (opts && "diffable" in opts) this.diffable = opts.diffable

  /**
   * The stack trace starting from the code that called `must`.
   *
   * @property stack
   */
  if (opts && opts.stack != null) Object.defineProperty(this, "stack", {
    value: opts.stack.replace(FIRST_LINE, this),
    configurable: true, writable: true
  })
  else if (Error.captureStackTrace)
    Error.captureStackTrace(this, opts && opts.caller || this.constructor)
}

AssertionError.prototype = Object.create(Error.prototype, {
  constructor: {value: AssertionError, configurable: true, writable: true}
})

AssertionError.prototype.name = "AssertionError"

/**
 * Some test runners (like [Mocha](http://visionmedia.github.io/mocha/)) expect
 * this property instead.
 *
 * @property showDiff
 * @alias diffable
 */
O.defineGetter(AssertionError.prototype, "showDiff", function() {
  return this.diffable
})