diff --git a/.babelrc b/.babelrc
new file mode 100644
index 0000000..c13c5f6
--- /dev/null
+++ b/.babelrc
@@ -0,0 +1,3 @@
+{
+  "presets": ["es2015"]
+}
diff --git a/.gitignore b/.gitignore
index f06235c..5f7c57e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,3 @@
 node_modules
 dist
+#lib
diff --git a/.npmignore b/.npmignore
new file mode 100644
index 0000000..0f30a4f
--- /dev/null
+++ b/.npmignore
@@ -0,0 +1 @@
+#src/
diff --git a/lib/assert.js b/lib/assert.js
new file mode 100644
index 0000000..60ce01f
--- /dev/null
+++ b/lib/assert.js
@@ -0,0 +1,96 @@
+'use strict';
+
+var _require = require('./helpers'),
+    isStream = _require.isStream,
+    isReadable = _require.isReadable,
+    isWritable = _require.isWritable,
+    waitUntilEndEventFired = _require.waitUntilEndEventFired,
+    TimeoutError = _require.TimeoutError;
+
+function extendTDDStyle(chai, utils) {
+  var assert = chai.assert,
+      AssertionError = chai.AssertionError;
+
+  /*
+   * Examples:
+   *   - assert.isStream(obj)
+   *   - assert.isNotStream(obj)
+   */
+
+  assert.isStream = function (actual) {
+    assert(isStream(actual), 'expected ' + actual + ' to be a Stream ');
+  };
+
+  assert.isNotStream = function (actual) {
+    assert(!isStream(actual), 'expected ' + actual + ' to not be a Stream ');
+  };
+
+  /*
+   * Examples:
+   *   - assert.isReadableStream(obj)
+   *   - assert.isNotReadableStream(obj)
+   */
+  assert.isReadableStream = function (actual) {
+    assert.isStream(actual);
+    assert(isReadable(actual), 'expected ' + actual + ' to be a ReadableStream ');
+  };
+
+  assert.isNotReadableStream = function (actual) {
+    assert.isStream(actual);
+    assert(!isReadable(actual), 'expected ' + actual + ' to not be a ReadableStream ');
+  };
+
+  /*
+   * Examples:
+   *   - assert.isWritableStream(obj)
+   *   - assert.isNotWritableStream(obj)
+   */
+  assert.isWritableStream = function (actual) {
+    assert.isStream(actual);
+    assert(isWritable(actual), 'expected ' + actual + ' to be a WritableStream ');
+  };
+
+  assert.isNotWritableStream = function (actual) {
+    assert.isStream(actual);
+    assert(!isWritable(actual), 'expected ' + actual + ' to not be a WritableStream ');
+  };
+
+  /*
+   * Examples:
+   *   - assert.streamWillEnd(stream);
+   *   - assert.streamWillNotEnd(stream);
+   */
+  assert.streamWillEnd = function (actual) {
+    return new Promise(function (onFulfilled) {
+      assert.isReadableStream(actual);
+      onFulfilled();
+    }).then(function () {
+      return waitUntilEndEventFired(actual, 1000);
+    }).catch(function (error) {
+      if (error instanceof TimeoutError) {
+        throw new AssertionError('expected the stream to end but not end');
+      }
+
+      throw error;
+    });
+  };
+
+  assert.streamWillNotEnd = function (actual) {
+    return new Promise(function (onFulfilled) {
+      assert.isReadableStream(actual);
+      onFulfilled();
+    }).then(function () {
+      return waitUntilEndEventFired(actual, 1000);
+    }).then(function () {
+      throw new AssertionError('expect the stream to not end but end');
+    }, function (error) {
+      if (error instanceof TimeoutError) {
+        return;
+      }
+
+      throw error;
+    });
+  };
+}
+
+module.exports = extendTDDStyle;
\ No newline at end of file
diff --git a/lib/browser.js b/lib/browser.js
new file mode 100644
index 0000000..66faa6c
--- /dev/null
+++ b/lib/browser.js
@@ -0,0 +1,15 @@
+'use strict';
+
+(function () {
+  var chaiStream = require('./index');
+
+  if (typeof define === 'function' && define.amd) {
+    // AMD
+    define(function () {
+      return chaiAsPromised;
+    });
+  } else {
+    chai.use(chaiAsPromised);
+    self.chaiAsPromised = chaiAsPromised;
+  }
+});
\ No newline at end of file
diff --git a/lib/expect.js b/lib/expect.js
new file mode 100644
index 0000000..173221b
--- /dev/null
+++ b/lib/expect.js
@@ -0,0 +1,82 @@
+'use strict';
+
+var _require = require('./helpers'),
+    isStream = _require.isStream,
+    isReadable = _require.isReadable,
+    isWritable = _require.isWritable,
+    waitUntilEndEventFired = _require.waitUntilEndEventFired,
+    TimeoutError = _require.TimeoutError;
+
+function extendExpectStyle(chai, utils) {
+  var Assertion = chai.Assertion,
+      AssertionError = chai.AssertionError;
+
+  /*
+   * Examples:
+   *   - expect(obj).to.be.a.Stream
+   *   - expect(obj).to.not.be.a.Stream
+   */
+
+  utils.addProperty(Assertion.prototype, 'Stream', function () {
+    var actual = this._obj;
+    this.assert(isStream(actual), 'expect #{this} to be a Stream', 'expect #{this} to not be a Stream');
+  });
+
+  /*
+   * Examples:
+   *   - expect(obj).to.be.a.ReadableStream
+   *   - expect(obj).to.not.be.a.ReadableStream
+   */
+  utils.addProperty(Assertion.prototype, 'ReadableStream', function () {
+    var actual = this._obj;
+
+    new Assertion(this._obj).to.be.a.Stream;
+
+    this.assert(isReadable(actual), 'expect #{this} to be a readable stream but got not readable', 'expect #{this} to not be a readable stream but got readable');
+  });
+
+  /*
+   * Examples:
+   *   - expect(obj).to.be.a.WritableStream
+   *   - expect(obj).to.not.be.a.WritableStream
+   */
+  utils.addProperty(Assertion.prototype, 'WritableStream', function () {
+    var actual = this._obj;
+
+    new Assertion(this._obj).to.be.a.Stream;
+
+    this.assert(isWritable(actual), 'expect #{this} to be a writable stream but got not writable', 'expect #{this} to not be a writable stream but got writable');
+  });
+
+  /*
+   * Examples:
+   *   - expect(obj).to.be.a.WritableStream
+   *   - expect(obj).to.not.be.a.WritableStream
+   */
+  utils.addProperty(Assertion.prototype, 'end', function () {
+    var _this = this;
+
+    var actual = this._obj;
+
+    return new Promise(function (onFulfilled) {
+      new Assertion(actual).to.be.a.ReadableStream;
+      onFulfilled();
+    }).then(function () {
+      return waitUntilEndEventFired(actual, 1000);
+    }).then(function () {
+      // For supporting .to.not.end
+      _this.assert(true, 'expected the stream to not end but end');
+      return actual;
+    }, function (error) {
+      if (error instanceof TimeoutError) {
+        // For supporting .to.not.end
+        _this.assert(false, 'expected the stream to end but not end');
+        return;
+      }
+
+      throw error;
+    });
+  });
+}
+
+module.exports = extendExpectStyle;
\ No newline at end of file
diff --git a/lib/helpers.js b/lib/helpers.js
new file mode 100644
index 0000000..26ff35b
--- /dev/null
+++ b/lib/helpers.js
@@ -0,0 +1,79 @@
+'use strict';
+
+var _createClass = function () { function defineProperties(target, props) { for (var i = 0; i < props.length; i++) { var descriptor = props[i]; descriptor.enumerable = descriptor.enumerable || false; descriptor.configurable = true; if ("value" in descriptor) descriptor.writable = true; Object.defineProperty(target, descriptor.key, descriptor); } } return function (Constructor, protoProps, staticProps) { if (protoProps) defineProperties(Constructor.prototype, protoProps); if (staticProps) defineProperties(Constructor, staticProps); return Constructor; }; }();
+
+function _classCallCheck(instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError("Cannot call a class as a function"); } }
+
+function _possibleConstructorReturn(self, call) { if (!self) { throw new ReferenceError("this hasn't been initialised - super() hasn't been called"); } return call && (typeof call === "object" || typeof call === "function") ? call : self; }
+
+function _inherits(subClass, superClass) { if (typeof superClass !== "function" && superClass !== null) { throw new TypeError("Super expression must either be null or a function, not " + typeof superClass); } subClass.prototype = Object.create(superClass && superClass.prototype, { constructor: { value: subClass, enumerable: false, writable: true, configurable: true } }); if (superClass) Object.setPrototypeOf ? Object.setPrototypeOf(subClass, superClass) : subClass.__proto__ = superClass; }
+
+var highland = require('highland');
+var Error = require('es6-error');
+
+function isStream(obj) {
+  return obj && typeof obj.pipe === 'function';
+}
+
+function isReadable(obj) {
+  // highland streams is readable but it do not have `read()`, so we cannot
+  // detect redability of highland streams by using it. But highland streams
+  // have a `resume()` and only readable streams have it. So we can detect
+  // readability of streams (including highland) by using `resume()`.
+  return obj && typeof obj.resume === 'function';
+}
+
+function isWritable(obj) {
+  return obj && typeof obj.write === 'function';
+}
+
+function waitUntilEndEventFired(stream, timeoutMsec) {
+  var isOutdated = false;
+  return new Promise(function (onFulfilled, onRejected) {
+    setTimeout(function () {
+      if (isOutdated) {
+        return;
+      }
+      isOutdated = true;
+      onRejected(TimeoutError.create(timeoutMsec));
+    }, timeoutMsec);
+
+    highland(stream).toArray(function (data) {
+      if (isOutdated) {
+        return;
+      }
+      isOutdated = true;
+      onFulfilled();
+    });
+  });
+}
+
+var TimeoutError = function (_Error) {
+  _inherits(TimeoutError, _Error);
+
+  function TimeoutError(msg) {
+    _classCallCheck(this, TimeoutError);
+
+    var _this = _possibleConstructorReturn(this, (TimeoutError.__proto__ || Object.getPrototypeOf(TimeoutError)).call(this, msg));
+
+    _this.message = msg;
+    return _this;
+  }
+
+  _createClass(TimeoutError, null, [{
+    key: 'create',
+    value: function create(timeoutMsec) {
+      return new TimeoutError('Timeout of ' + timeoutMsec + ' ms exceeded');
+    }
+  }]);
+
+  return TimeoutError;
+}(Error);
+
+module.exports = {
+  isStream: isStream,
+  isReadable: isReadable,
+  isWritable: isWritable,
+  waitUntilEndEventFired: waitUntilEndEventFired,
+  TimeoutError: TimeoutError
+};
\ No newline at end of file
diff --git a/lib/index.js b/lib/index.js
new file mode 100644
index 0000000..ea299e0
--- /dev/null
+++ b/lib/index.js
@@ -0,0 +1,11 @@
+'use strict';
+
+var Promise = require('es6-promise');
+var highland = require('highland');
+
+function chaiStream(chai, utils) {
+  require('./assert')(chai, utils);
+  require('./expect')(chai, utils);
+}
+
+module.exports = chaiStream;
\ No newline at end of file
diff --git a/package.json b/package.json
index 645c64d..131d89e 100644
--- a/package.json
+++ b/package.json
@@ -2,10 +2,11 @@
   "name": "chai-stream",
   "version": "0.0.0",
   "description": "Extends Chai with assertions about streams.",
-  "main": "src/index.js",
+  "main": "lib/index.js",
   "scripts": {
-    "prepublish": "mkdir -p dist && browserify src/browser.js -t babelify --outfile dist/chai-stream.js",
-    "test": "mocha --compilers js:mocha-babel tests --timeout 10000"
+    "compile": "babel -d lib/ src/",
+    "prepublish": "npm run compile && mkdir -p dist && browserify src/browser.js -t babelify --outfile dist/chai-stream.js",
+    "test": "npm run compile && mocha --compilers js:babel-register tests --timeout 10000"
   },
   "repository": {
     "type": "git",
@@ -24,18 +25,22 @@
   },
   "homepage": "https://github.com/Kuniwak/chai-stream",
   "dependencies": {
+    "es6-error": "^4.0.0",
     "es6-promise": "^3.0.2",
+    "es6-error": "^4.0.0",
     "highland": "^2.5.1"
   },
   "devDependencies": {
-    "babel-runtime": "^5.8.20",
-    "babelify": "^6.3.0",
+    "babel-cli": "^6.18.0",
+    "babel-core": "^6.18.2",
+    "babel-preset-es2015": "^6.18.0",
+    "babel-register": "^6.18.0",
+    "babelify": "",
     "browserify": "^11.0.1",
     "chai": "^3.2.0",
     "chai-as-promised": "^5.1.0",
     "eslint": "^1.3.1",
     "jscs": "^2.1.1",
-    "mocha": "^2.2.5",
-    "mocha-babel": "^3.0.0"
+    "mocha": "^2.2.5"
   }
 }
diff --git a/src/helpers.js b/src/helpers.js
index 85458aa..b41822a 100644
--- a/src/helpers.js
+++ b/src/helpers.js
@@ -1,4 +1,5 @@
 const highland = require('highland');
+const Error = require('es6-error');
 
 function isStream(obj) {
   return obj && typeof obj.pipe === 'function';