patch function Scan to support int,int8,int16,int32 (#1)

[corelmax]

if i have an table on RDBMS and i need to query it and map to struct looks like this

type Data struct {
 A decimal.Decimal
 B decimal.Decimal
 C decimal.Decimal
}

and i don't want to test with actual connection to database. so i create SqlRows implementation like this

// Scan ...
func (inst *MockScanner) Scan(src ...interface{}) error {
	for i, d := range src {
		switch d := d.(type) {
		case *int:
			*d = inst.data[i].(int)
		case *string:
			*d = inst.data[i].(string)
		case *float32:
			*d = inst.data[i].(float32)
		case *float64:
			*d = inst.data[i].(float64)
		default:
			if scanner, ok := d.(sql.Scanner); ok {
				if err := scanner.Scan(inst.data[i]); err != nil {
					return err
				}
			}
		}
	}

	return nil
}

then, i create function like this

func MapData(rows *sql.SqlRows) (*Data, error) {
  var out Data
  err := rows.Scan(&out.A, &out.B, &out.C)
  return &out, err
}

So, I able to test this function without actual query on database like this

mock := NewMockScanner(1, 2, 3) // now support int. so, it doesn't need to be NewMockScanner(int64(1), ...) or NewMockScanner(decimal.NewFromFloat(1), ...) 
out,err := MapData(mock)
So(out.A, ShouldEqual, decimal.NewFromFloat(1))
...

someone might think this is pointless. but, if someone have to deal with bank's project and need to write some tests for function which deal with hundred of fields (and all of them have to be mocked), this should made a point.

[njason]

One small ask, otherwise looks good.

[njason]

Can you remove this comment, it seems unnecessary.