Operations on go-sqlmock.Driver fail with: expected a connection to be available, but it is not

[fho]

Hello,

I'm working on a package that wraps an sql.Driver and adds functionality.
To test it, I'm trying to use go-sqlmock.
I'm running into the issue that if I wrap the go-sqlmock Driver, all operations fail with the error:
expected a connection to be available, but it is not

I'm accessing the driver via:

db, _, _ := sqlmock.New()
db.Driver()

This can be reproduced e.g. via sqlmw:

package dddbmock_test

import (
	"database/sql"
	"testing"

	"github.com/DATA-DOG/go-sqlmock"
	"github.com/ngrok/sqlmw"
)

func TestMWWrap(t *testing.T) {
	db, _, err := sqlmock.New()
	if err != nil {
		t.Fatal("sqlmock new failed:", err)
	}

	sql.Register(
		"mwdriver",
		sqlmw.Driver(db.Driver(), &sqlmw.NullInterceptor{}),
	)

	db, err = sql.Open("mydriver", "")
	if err != nil {
		t.Fatal("opening driver failed:", err)
	}

	if err := db.Ping(); err != nil {
		t.Error("ping failed", err)
	}
}

Without using other external packages and mimicking the wrapping behavior instead it can be reproduced like:

package dddbmock_test

import (
	"database/sql"
	"testing"

	"github.com/DATA-DOG/go-sqlmock"
)

func TestRegister(t *testing.T) {
	db, _, err := sqlmock.New(sqlmock.MonitorPingsOption(true))
	if err != nil {
		t.Fatal("sqlmock new failed:", err)
	}

	sql.Register("mydriver", db.Driver())

	db, err = sql.Open("mydriver", "")
	if err != nil {
		t.Fatal("opening driver failed:", err)
	}

	if err := db.Ping(); err != nil {
		t.Error("ping failed", err)
	}

	if _, err := db.Exec(""); err != nil {
		t.Error("exec failed", err)
	}
}

The comment #83 (comment) seems to be about the same issue.
I guess it's not intended to be used like that, but it would be awesome to support operations on the go-sqlmock Driver.

[l3pp4rd]

Hi, maybe you are willing to contribute this patch? Haven’t used golang for more than a year, would be difficult to find a willing to

[fho]

@l3pp4rd depends on the effort :-). I ended up writing my own simple mock instead, that works okayish for my current usecase.
Do you maybe have an idea what the cause it how it could be fixed?

[dolmen]

The first code has a typo in the driver name: mwdriver vs mydriver.

[dolmen]

Here is a hack (unsupported): use the internal DSN:

db, err = sql.Open("mydriver", "sqlmock_db_0")

Example on the Go Playground