Did you actually write explicit transaction isolation levels in Go code?

Yes, it is possible to explicitly set the transaction isolation level in Go code, although this depends on the database driver and package used.

For example, with the database/sql package, you can use the BeginTx method with the sql.TxOptions parameter, where you can specify the isolation level through the Isolation field.

Example:

import (
    "context"
    "database/sql"
)

func example(db *sql.DB) error {
    ctx := context.Background()
    txOptions := &sql.TxOptions{
        Isolation: sql.LevelSerializable, // explicit isolation level
        ReadOnly:  false,
    }
    tx, err := db.BeginTx(ctx, txOptions)
    if err != nil {
        return err
    }
    defer tx.Rollback() // rollback if not committed

    // operations with tx

    return tx.Commit()
}

Thus, you can control the transaction isolation level directly from Go code.