WARN [middleware:karma]: Invalid file type, defaulting to js. ts : <p>When I run unit testing via karma, I got those warning:</p>

<pre><code>12 02 2019 14:01:05.740:WARN [middleware:karma]: Invalid file type, defaulting to js. ts
12 02 2019 14:01:05.741:WARN [middleware:karma]: Invalid file type, defaulting to js. ts
</code></pre>

<p>I assumed that the type of the <code>karma.conf.js</code> file caused the issue, so I changed it to <code>karma.conf.ts</code>.</p>

<p>However the issue still happened, so it would be great if someone can tell me how to disable this warning.</p>

<p>Below is my karma.conf.ts file</p>

<pre><code>module.exports = function karmaConfig(config) {
    config.set({

        singleRun: true,

        frameworks: [
            'jasmine'
        ],

        files: [
            'sdk/**/*.spec.ts'
        ],

        preprocessors: {
            'sdk/**/*.spec.ts': ['webpack', 'sourcemap'],
            'sdk/**/!(*.spec).ts': ['coverage']
        },

        browsers: [
            'PhantomJS'
        ],

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

        coverageReporter: {
            dir: 'coverage/',
            reporters: [
                { type: 'text-summary' },
                { type: 'html' },
                {
                    type: 'lcov',
                    dir: 'reports',
                    subdir: 'coverage'
                }
            ]
        },

        junitReporter: {
            outputFile: 'reports/junit/TEST-karma.xml',
            useBrowserName: false
        },

        transports: ['polling'],

        webpack: require('./webpack.config'),

        webpackMiddleware: {
            stats: 'errors-only'
        },

        logLevel: config.LOG_INFO,

    });
};
</code></pre>

<p>I use webpack <code>4.16.5</code> and karma <code>4.0.0</code></p>
