javascript - Coffeescript でカルマを使用するとエラーが発生する: JSON.stringify 循環構造のシリアライゼーション

Question

Coffeescript で karma を実行すると、このエラーが発生するのはなぜですか?

$ karma run
WARN [watcher]: Pattern "/home/yang/reactive.coffee/test/mock/**/*.js"
does not match any file.
WARN [watcher]: Pattern "/home/yang/reactive.coffee/src/**/*.js" does
not match any file.
PhantomJS 1.9 (Linux) ERROR
        TypeError: JSON.stringify cannot serialize cyclic structures.
        at http://localhost:8080/socket.io/socket.io.js:1066
PhantomJS 1.9 (Linux): Executed 0 of 0 ERROR (0.212 secs / 0 secs)
PhantomJS 1.9 (Linux) ERROR
        TypeError: JSON.stringify cannot serialize cyclic structures.
        at http://localhost:8080/socket.io/socket.io.js:1066
PhantomJS 1.9 (Linux): Executed 0 of 0 ERROR (0.212 secs / 0 secs)

Firefox に切り替えたときにも発生します。

Firefox 20.0 (Linux) ERROR
        TypeError: cyclic object value
        at http://localhost:8081/socket.io/socket.io.js:1066

CS から JS に切り替えると、エラーはなくなります。

詳細 - 他に役立つ情報があれば教えてください。

$ karma --version
Karma version: 0.8.5

$ tree src
src
└── reactive.coffee

0 directories, 1 file

$ tree test
test
└── spec
    └── test_reactive.js

1 directory, 1 file

$ cat karma.conf.js
// Karma configuration

// base path, that will be used to resolve files and exclude
basePath = '';

// list of files / patterns to load in the browser
files = [
  JASMINE,
  JASMINE_ADAPTER,
  'src/*.coffee',
  'src/**/*.js',
  'test/mock/**/*.js',
  'test/spec/**/*.js'
];

// list of files to exclude
exclude = [];

// test results reporter to use
// possible values: dots || progress || growl
reporters = ['progress'];

// web server port
port = 8080;

// cli runner port
runnerPort = 9100;

// enable / disable colors in the output (reporters and logs)
colors = true;

// level of logging
// possible values: LOG_DISABLE || LOG_ERROR || LOG_WARN || LOG_INFO
|| LOG_DEBUG
logLevel = LOG_INFO;

// enable / disable watching file and executing tests whenever any file changes
autoWatch = false;

// Start these browsers, currently available:
// - Chrome
// - ChromeCanary
// - Firefox
// - Opera
// - Safari (only Mac)
// - PhantomJS
// - IE (only Windows)
browsers = ['PhantomJS'];

// If browser does not capture in given timeout [ms], kill it
captureTimeout = 10000;

// Continuous Integration mode
// if true, it capture browsers, run tests and exit
singleRun = false;