I am configuring my Karma amd mocha framework with grunt in my project. When I am running karma start I am getting below-mentioned error.

I am getting this error in my console while running command : Karma start

TypeError: expect(...).to.be is not a function

My Karma.confjs

// Karma configuration

// Generated on Fri Nov 27 2015 11:48:47 GMT+0530 (India Standard Time)



module.exports = function(config) {

  config.set({



    // base path that will be used to resolve all patterns (eg. files, exclude)

    basePath: '',





    // frameworks to use

    // available frameworks: https://npmjs.org/browse/keyword/karma-adapter

    frameworks: ['mocha', 'chai'],





    // list of files / patterns to load in the browser

    files: [

      'bower_components/angular/angular.js',

      'bower_components/angular-mocks/angular-mocks.js',

      'app/*.js',

      // 'test/specs/*.js',

      'test/specs/array.js',

      // 'test/specs/myCtlr-spec.js',

      //'test/*.js'

    ],





    // list of files to exclude

    exclude: [

    ],





    // preprocess matching files before serving them to the browser

    // available preprocessors: https://npmjs.org/browse/keyword/karma-preprocessor

    preprocessors: {

    },





    // test results reporter to use

    // possible values: 'dots', 'progress'

    // available reporters: https://npmjs.org/browse/keyword/karma-reporter

    reporters: ['progress','coverage'],



    preprocessors: {

        'src/app/**/*.js': ['coverage']

    },

    coverageReporter: {

        type: 'lcov',

        dir: 'coverage/'

    },



    // web server port

    port: 9876,





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

    colors: true,





    // level of logging

    // possible values: config.LOG_DISABLE || config.LOG_ERROR || config.LOG_WARN || config.LOG_INFO || config.LOG_DEBUG

    logLevel: config.LOG_INFO,





    // enable / disable watching file and executing tests whenever any file changes

    autoWatch: true,





    // start these browsers

    // available browser launchers: https://npmjs.org/browse/keyword/karma-launcher

    // browsers: ['PhantomJS', 'Chrome'],

    browsers: ['Chrome'],





    // Continuous Integration mode

    // if true, Karma captures browsers, runs the tests and exits

    singleRun: false,



    // Concurrency level

    // how many browser should be started simultanous

    concurrency: Infinity

  })

}

My array.js test

// var expect = require('chai').expect;



describe(Mocha: The 'toBe' matcher compares with ===, function() {

  it(and has a positive case, function() {

    expect(true).to.be(true);

  });



  it(and can have a negative case, function() {

    expect(false).not.to.be(true);

  });

});

Please suggest what I am missing.