Angular 4 Karma testing error

I want to make Karma tests on my Angular 4 application. When I leave the tests simple without importing anything they succeed. For example:

describe('Sample test', () => {
    it('should pass', () => {
        expect(1 + 1).toBe(2);
    });
});

However, when I try to import a class which is in the same folder like so:

import { ApiResponseTimeRepository } from './ApiResponseTimeRepository';

I get an error saying:

Chrome 58.0.3029 (Windows 10 0.0.0) ERROR
  Uncaught SyntaxError: Unexpected token import
  at services/TestRepositories.spec.ts:1

For reference, my class looks like this:

...
imports
...

@Injectable()
export class ApiResponseTimeRepository {
    ...
    code
    ...
}

And here is karma.conf.js :

// Karma configuration
// Generated on Mon Jun 12 2017 14:21:41 GMT+0200 (Central European Daylight Time)

module.exports = function (config) {
    config.set({

        // base path that will be used to resolve all patterns (eg. files, exclude)
        basePath: 'src/app',


        // frameworks to use
        // available frameworks: http://ift.tt/1ft83uu
        frameworks: ['jasmine'],


        // list of files / patterns to load in the browser
        files: [
            { pattern: '**/*.spec.ts' }
        ],


        // list of files to exclude
        exclude: [
        ],


        // preprocess matching files before serving them to the browser
        // available preprocessors: http://ift.tt/1gyw6MG
        preprocessors: {
        },


        // test results reporter to use
        // possible values: 'dots', 'progress'
        // available reporters: http://ift.tt/1ft83KQ
        reporters: ['progress'],


        // 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: http://ift.tt/1ft83KU
        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 simultaneous
        concurrency: Infinity,

        mime: {
            'text/x-typescript': ['ts', 'tsx']
        }
    });
};