You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: exportcsv_test.go
    path of file: ./repos/cockroach/pkg/sql/importer
    
    the code of the file until where you have to start completion: // Copyright 2018 The Cockroach Authors.
//
// Use of this software is governed by the Business Source License
// included in the file licenses/BSL.txt.
//
// As of the Change Date specified in that file, in accordance with
// the Business Source License, use of this software will be governed
// by the Apache License, Version 2.0, included in the file
// licenses/APL.txt.

package importer_test

import 
    
func TestExportNullWithEmptyNullAs(t *testing.T) {
	defer leaktest.AfterTest(t)()
	defer log.Scope(t).Close(t)

	ctx := context.Background()
	dir, cleanup := testutils.TempDir(t)
	defer cleanup()

	tc := testcluster.StartTestCluster(
		t, 1, base.TestClusterArgs{ServerArgs: base.TestServerArgs{ExternalIODir: dir}})
	defer tc.Stopper().Stop(ctx)

	conn := tc.Conns[0]
	db := sqlutils.MakeSQLRunner(conn)

	// Set up dummy accounts table with NULL value
	db.Exec(t, `
		CREATE TABLE accounts (id INT PRIMARY KEY, balance INT);
		INSERT INTO accounts VALUES (1, NULL), (2, 8);
	`)

	// Case when `nullas` option is unspecified: expect error
	const stmtWithoutNullas = "EXPORT INTO CSV 'nodelocal://1/t' FROM SELECT * FROM accounts"
	db.ExpectErr(t, "NULL value encountered during EXPORT, "+
		"use `WITH nullas` to specify the string representation of NULL", stmtWithoutNullas)

	// Case when `nullas` option is specified: operation is successful and NULLs are encoded to "None"
	const stmtWithNullas = `EXPORT INTO CSV 'nodelocal://1/t' WITH nullas="None" FROM SELECT * FROM accounts`
	db.Exec(t, stmtWithNullas)
	contents := readFileByGlob(t, filepath.Join(dir, "t", exportFilePattern))
	require.Equal(t, "1,None\n2,8\n", string(contents))

	// Verify successful IMPORT statement `WITH nullif="None"` to complete round trip
	const importStmt = `IMPORT INTO accounts2 CSV DATA ('nodelocal://1/t/export*-n*.0.csv') WITH nullif="None"`
	db.Exec(t, `CREATE TABLE accounts2(id INT PRIMARY KEY, balance INT)`)
	db.Exec(t, importStmt)
	db.CheckQueryResults(t,
		"SELECT * FROM accounts2", db.QueryStr(t, "SELECT * FROM accounts"),
	)
}