How to use the oracledb.fetchAsString function in oracledb

afterEach('clear the By type specification', function(done) {
      oracledb.fetchAsString = [];
      done();
    }); // afterEach

afterEach('clear the By type specification', function(done) {
      oracledb.fetchAsString = [];
      done();
    }); // afterEach

function change(cb) {
          oracledb.fetchAsString = [ oracledb.DATE, oracledb.NUMBER ];
          cb();
        },
        function test(cb) {

it('28.1.5 columns fetched from REF CURSORS can be mapped by oracledb.fetchAsString', function(done) {
      oracledb.fetchAsString = [ oracledb.NUMBER ];
      assist.verifyRefCursorWithFetchAsString(connection, tableName, numbers, done);
    });
  });

it('36.1.5 columns fetched from REF CURSORS can be mapped by oracledb.fetchAsString', function(done) {
      oracledb.fetchAsString = [ oracledb.DATE ];
      assist.verifyRefCursorWithFetchAsString(connection, tableName, dates, done);
    });

after('restore the values', function() {
      oracledb.poolMin          = defaultValues.poolMin;
      oracledb.poolMax          = defaultValues.poolMax;
      oracledb.poolIncrement    = defaultValues.poolIncrement;
      oracledb.poolTimeout      = defaultValues.poolTimeout;
      oracledb.maxRows          = defaultValues.maxRows;
      oracledb.fetchArraySize   = defaultValues.fetchArraySize;
      oracledb.autoCommit       = defaultValues.autoCommit;
      oracledb.connectionClass  = defaultValues.connectionClass;
      oracledb.externalAuth     = defaultValues.externalAuth;
      oracledb.fetchAsString    = defaultValues.fetchAsString;
      oracledb.outFormat        = defaultValues.outFormat;
      oracledb.lobPrefetchSize  = defaultValues.lobPrefetchSize;
      oracledb.queueTimeout     = defaultValues.queueTimeout;
      oracledb.stmtCacheSize    = defaultValues.stmtCacheSize;
      oracledb.poolPingInterval = defaultValues.poolPingInterval;
      oracledb.fetchAsBuffer    = defaultValues.fetchAsBuffer;
      oracledb.edition          = defaultValues.edition;
      oracledb.events           = defaultValues.events;
    });

after(function(done) {
      oracledb.fetchAsString = [];
      connection.execute(
        "DROP table " + tableName + " PURGE",
        function(err) {
          should.not.exist(err);
          done();
        }
      );
    });

after(function(done) {
      oracledb.fetchAsString = [];
      connection.execute(
        "DROP table " + tableName + " PURGE",
        function(err) {
          should.not.exist(err);
          done();
        }
      );
    });

before('save the default values', function() {
      defaultValues.poolMin          = oracledb.poolMin;
      defaultValues.poolMax          = oracledb.poolMax;
      defaultValues.poolIncrement    = oracledb.poolIncrement;
      defaultValues.poolTimeout      = oracledb.poolTimeout;
      defaultValues.maxRows          = oracledb.maxRows;
      defaultValues.fetchArraySize   = oracledb.fetchArraySize;
      defaultValues.autoCommit       = oracledb.autoCommit;
      defaultValues.connectionClass  = oracledb.connectionClass;
      defaultValues.externalAuth     = oracledb.externalAuth;
      defaultValues.fetchAsString    = oracledb.fetchAsString;
      defaultValues.outFormat        = oracledb.outFormat;
      defaultValues.lobPrefetchSize  = oracledb.lobPrefetchSize;
      defaultValues.queueTimeout     = oracledb.queueTimeout;
      defaultValues.stmtCacheSize    = oracledb.stmtCacheSize;
      defaultValues.poolPingInterval = oracledb.poolPingInterval;
      defaultValues.fetchAsBuffer    = oracledb.fetchAsBuffer;
      defaultValues.edition          = oracledb.edition;
      defaultValues.events           = oracledb.events;
    });

function(cb) {
          var defaultValue = [];
          (oracledb.fetchAsString).should.eql(defaultValue);
          cb();
        }
      ], done);