extend mocha dot reporter with log4js capture

logreport.js

var log4js = require('log4js'),
    Base = require('mocha/lib/reporters/base'),
    Dot = require('mocha/lib/reporters/dot'),
    diff = require('diff'),
    ms = require('mocha/lib/ms'),
    color = Base.color;

function LogReport(runner) {
    var captured = [],
        layout = log4js.layouts.colouredLayout;

    Dot.call(this, runner);

    runner.on('start', function () {
        log4js.clearAppenders();
        log4js.addAppender(function (logEvent) {
            captured.push(layout(logEvent));
        });
    });

    runner.on('test', function () {
        captured = [];
    });

    runner.on('fail', function (test) {
        if (captured.length) {
            test.capturedLog = captured;
        }
    });
}

/**
 * Check that a / b have the same type.
 *
 * @param {Object} a
 * @param {Object} b
 * @return {Boolean}
 * @api private
 */
function sameType(a, b) {
  a = Object.prototype.toString.call(a);
  b = Object.prototype.toString.call(b);
  return a == b;
}

/**
 * Returns a string with all invisible characters in plain text
 *
 * @param {String} line
 * @return {String}
 * @api private
 */
function escapeInvisibles(line) {
    return line.replace(/\t/g, '<tab>')
               .replace(/\r/g, '<CR>')
               .replace(/\n/g, '<LF>\n');
}

/**
 * Color lines for `str`, using the color `name`.
 *
 * @param {String} name
 * @param {String} str
 * @return {String}
 * @api private
 */
function colorLines(name, str) {
  return str.split('\n').map(function(str){
    return color(name, str);
  }).join('\n');
}

/**
 * Returns an inline diff between 2 strings with coloured ANSI output
 *
 * @param {Error} Error with actual/expected
 * @return {String} Diff
 * @api private
 */
function inlineDiff(err, escape) {
  var msg = errorDiff(err, 'WordsWithSpace', escape);

  // linenos
  var lines = msg.split('\n');
  if (lines.length > 4) {
    var width = String(lines.length).length;
    msg = lines.map(function(str, i){
      return pad(++i, width) + ' |' + ' ' + str;
    }).join('\n');
  }

  // legend
  msg = '\n'
    + color('diff removed', 'actual')
    + ' '
    + color('diff added', 'expected')
    + '\n\n'
    + msg
    + '\n';

  // indent
  msg = msg.replace(/^/gm, '      ');
  return msg;
}

/**
 * Returns a unified diff between 2 strings
 *
 * @param {Error} Error with actual/expected
 * @return {String} Diff
 * @api private
 */
function unifiedDiff(err, escape) {
  var indent = '      ';
  function cleanUp(line) {
    if (escape) {
      line = escapeInvisibles(line);
    }
    if (line[0] === '+') return indent + colorLines('diff added', line);
    if (line[0] === '-') return indent + colorLines('diff removed', line);
    if (line.match(/\@\@/)) return null;
    if (line.match(/\\ No newline/)) return null;
    else return indent + line;
  }
  function notBlank(line) {
    return line != null;
  }
  msg = diff.createPatch('string', err.actual, err.expected);
  var lines = msg.split('\n').splice(4);
  return '\n      '
         + colorLines('diff added',   '+ expected') + ' '
         + colorLines('diff removed', '- actual')
         + '\n\n'
         + lines.map(cleanUp).filter(notBlank).join('\n');
}

/**
 * Outut the given `failures` as a list.
 *
 * @param {Array} failures
 * @api public
 */
function list(failures) {
  console.error();
  failures.forEach(function(test, i){
    // format
    var fmt = color('error title', '  %s) %s:\n')
      + color('error message', '     %s')
      + color('error stack', '\n%s\n');

    // msg
    var err = test.err
      , message = err.message || ''
      , stack = err.stack || message
      , index = stack.indexOf(message) + message.length
      , msg = stack.slice(0, index)
      , actual = err.actual
      , expected = err.expected
      , escape = true;

    // uncaught
    if (err.uncaught) {
      msg = 'Uncaught ' + msg;
    }

    // explicitly show diff
    if (err.showDiff && sameType(actual, expected)) {
      escape = false;
      err.actual = actual = stringify(actual);
      err.expected = expected = stringify(expected);
    }

    // actual / expected diff
    if ('string' == typeof actual && 'string' == typeof expected) {
      fmt = color('error title', '  %s) %s:\n%s') + color('error stack', '\n%s\n');
      var match = message.match(/^([^:]+): expected/);
      msg = match ? '\n      ' + color('error message', match[1]) : '';

      if (exports.inlineDiffs) {
        msg += inlineDiff(err, escape);
      } else {
        msg += unifiedDiff(err, escape);
      }
    }

    if (test.capturedLog) {
        msg += '\n  Captured log messages:\n';
        test.capturedLog.forEach(function (log) {
            msg += '  ' + log;
        });
    }

    // indent stack trace without msg
    stack = stack.slice(index ? index + 1 : index)
      .replace(/^/gm, '  ');

    console.error(fmt, (i + 1), test.fullTitle(), msg, stack);
  });
}

LogReport.prototype = Object.create(Dot.prototype);

LogReport.prototype.epilogue = function () {
  var stats = this.stats;
  var tests;
  var fmt;

  console.log();

  // passes
  fmt = color('bright pass', ' ')
    + color('green', ' %d passing')
    + color('light', ' (%s)');

  console.log(fmt,
    stats.passes || 0,
    ms(stats.duration));

  // pending
  if (stats.pending) {
    fmt = color('pending', ' ')
      + color('pending', ' %d pending');

    console.log(fmt, stats.pending);
  }

  // failures
  if (stats.failures) {
    fmt = color('fail', '  %d failing');

    console.error(fmt,
      stats.failures);
    list(this.failures);
    console.error();
  }
};

module.exports = LogReport;