Remove TestMain from package pkg/sqlfs

[wangkuiyi]

In pkg/sqlfs/sqlfile_test.go, there defines a TestMain` function

sqlflow/pkg/sqlfs/sqlfile_test.go

Lines 146 to 174 in 68ae7c6

	func TestMain(m *testing.M) {
	testDriver = getEnv("SQLFLOW_TEST_DB", "mysql")
	var e error
	switch testDriver {
	case "mysql":
	cfg := &mysql.Config{
	User: getEnv("SQLFLOW_TEST_DB_MYSQL_USER", "root"),
	Passwd: getEnv("SQLFLOW_TEST_DB_MYSQL_PASSWD", "root"),
	Net: getEnv("SQLFLOW_TEST_DB_MYSQL_NET", "tcp"),
	Addr: getEnv("SQLFLOW_TEST_DB_MYSQL_ADDR", "127.0.0.1:3306"),
	AllowNativePasswords: true,
	}
	testDB, e = sql.Open("mysql", cfg.FormatDSN())
	assertNoErr(e)
	_, e = testDB.Exec(fmt.Sprintf("CREATE DATABASE IF NOT EXISTS %s;", testDatabaseName))
	assertNoErr(e)
	defer testDB.Close()
	case "hive":
	testDB, e = sql.Open("hive", "root:root@localhost:10000/churn")
	assertNoErr(e)
	_, e = testDB.Exec(fmt.Sprintf("CREATE DATABASE IF NOT EXISTS %s;", testDatabaseName))
	assertNoErr(e)
	defer testDB.Close()
	default:
	assertNoErr(fmt.Errorf("unrecognized environment variable SQLFLOW_TEST_DB %s", testDriver))
	}
	os.Exit(m.Run())
	}

Currently, we suffer from the fact that we have to restrict serial execution unit tests in our CI with go test -p 1 -- for more details, please refer to #1283 (comment)

The requirement of -p 1 is possibly due to the use of a global database and tables during testing. To remove the restriction, we can start from rewrite TestMain into a new and reusable function createDatabase. In each test case, we can call this function.