How to use the @optimizely/js-sdk-logging.setLogLevel function in @optimizely/js-sdk-logging

var hasLogger = false;
      config = config || {};

      // TODO warn about setting per instance errorHandler / logger / logLevel
      if (config.errorHandler) {
        logging.setErrorHandler(config.errorHandler);
      }
      if (config.logger) {
        // only set a logger in node if one is provided, by not setting we are noop-ing
        hasLogger = true;
        logging.setLogHandler(config.logger);
        // respect the logger's shouldLog functionality
        logging.setLogLevel(logging.LogLevel.NOTSET);
      }
      if (config.logLevel !== undefined) {
        logging.setLogLevel(config.logLevel);
      }

      try {
        configValidator.validate(config);
        config.isValidInstance = true;
      } catch (ex) {
        if (hasLogger) {
          logger.error(ex);
        } else {
          console.error(ex.message);
        }
        config.isValidInstance = false;
      }

      config = fns.assign(
        {

createInstance: function(config) {
    try {
      config = config || {};

      // TODO warn about setting per instance errorHandler / logger / logLevel
      if (config.errorHandler) {
        logging.setErrorHandler(config.errorHandler);
      }
      if (config.logger) {
        logging.setLogHandler(config.logger);
        // respect the logger's shouldLog functionality
        logging.setLogLevel(logging.LogLevel.NOTSET);
      }
      if (config.logLevel !== undefined) {
        logging.setLogLevel(config.logLevel);
      }

      try {
        configValidator.validate(config);
        config.isValidInstance = true;
      } catch (ex) {
        logger.error(ex);
        config.isValidInstance = false;
      }

      // Explicitly check for null or undefined
      // prettier-ignore
      if (config.skipJSONValidation == null) { // eslint-disable-line eqeqeq
        config.skipJSONValidation = true;
      }

createInstance: function(config) {
    try {
      config = config || {};

      // TODO warn about setting per instance errorHandler / logger / logLevel
      if (config.errorHandler) {
        logging.setErrorHandler(config.errorHandler);
      }
      if (config.logger) {
        logging.setLogHandler(config.logger);
        // respect the logger's shouldLog functionality
        logging.setLogLevel(logging.LogLevel.NOTSET);
      }
      if (config.logLevel !== undefined) {
        logging.setLogLevel(config.logLevel);
      }

      try {
        configValidator.validate(config);
        config.isValidInstance = true;
      } catch (ex) {
        logger.error(ex);
        config.isValidInstance = false;
      }

      // Explicitly check for null or undefined
      // prettier-ignore
      if (config.skipJSONValidation == null) { // eslint-disable-line eqeqeq
        config.skipJSONValidation = true;
      }

beforeEach(function() {
    sinon.stub(datafileManager, 'HttpPollingDatafileManager').returns({
      start: sinon.stub(),
      stop: sinon.stub(),
      get: sinon.stub().returns(null),
      on: sinon.stub().returns(function() {}),
      onReady: sinon.stub().returns({ then: function() {} }),
    });
    globalStubErrorHandler = {
      handleError: sinon.stub(),
    };
    logging.setErrorHandler(globalStubErrorHandler);
    logging.setLogLevel('notset');
    stubLogHandler = {
      log: sinon.stub(),
    };
    logging.setLogHandler(stubLogHandler);
  });