feature: Add WithTxOptions() to ExpectBegin

[smoynes]

It would be really handy if sqlmock.ExpectBegin() allowed the user to verify the options passed to BeginTx().

Proposal

• add txOptions *TxOptions field to ExpectedBegin:

  go-sqlmock/expectations.go

  Line 54 in 3476f31

  type ExpectedBegin struct {

• set ExpectedBegin.txOptions in new method (*ExpectedBegin).WithTxOptions(sql.TxOptions)
• verify expectation in BeginTx():

  go-sqlmock/sqlmock_go18.go

  Line 68 in 3476f31

  func (c *sqlmock) BeginTx(ctx context.Context, opts driver.TxOptions) (driver.Tx, error) {

Use-cases

Verifying transaction isolation level:

db, mock, err := sqlmock.New()
defer mock.ExpectationsWereMet()

txOpts := sql.TxOptions{Isolation: sql.LevelReadUncommitted}
mock.ExpectBegin().WithTxOptions(txOpts)

tx, err := db.BeginTx(context.TODO(), &txOpts)

Verifying read-only transactions:

db, mock, err := sqlmock.New()
defer mock.ExpectationsWereMet()

txOpts := sql.TxOptions{ReadOnly: true}
mock.ExpectBegin().WithTxOptions(txOpts)

tx, err := db.BeginTx(context.TODO(), &txOpts)