chore: enable Last flag in tests and check for only one dialect (#485)

Author: olavloite

driver.go

@@ -18,6 +18,7 @@ import (
 	"context"
 	"database/sql"
 	"database/sql/driver"
+	"errors"
 	"fmt"
 	"io"
 	"log/slog"
@@ -38,6 +39,7 @@ import (
 	"cloud.google.com/go/spanner/apiv1/spannerpb"
 	"github.com/google/uuid"
 	"github.com/googleapis/gax-go/v2"
+	"google.golang.org/api/iterator"
 	"google.golang.org/api/option"
 	"google.golang.org/api/option/internaloption"
 	"google.golang.org/grpc"
@@ -766,6 +768,13 @@ func determineDialect(ctx context.Context, client *spanner.Client) (databasepb.D
 			if err := row.Columns(&dialectName); err != nil {
 				return databasepb.DatabaseDialect_DATABASE_DIALECT_UNSPECIFIED, err
 			}
+			if _, err := it.Next(); !errors.Is(err, iterator.Done) {
+				if err == nil {
+					return databasepb.DatabaseDialect_DATABASE_DIALECT_UNSPECIFIED, fmt.Errorf("more than one dialect result returned")
+				} else {
+					return databasepb.DatabaseDialect_DATABASE_DIALECT_UNSPECIFIED, err
+				}
+			}
 			if dialect, ok := databasepb.DatabaseDialect_value[dialectName]; ok {
 				return databasepb.DatabaseDialect(dialect), nil
 			} else {

testutil/inmem_spanner_server.go

@@ -162,19 +162,22 @@ func (s *StatementResult) ToPartialResultSets(resumeToken []byte) (result []*spa
 			} else {
 				rt = s.ResumeTokens[startIndex]
 			}
-			result = append(result, &spannerpb.PartialResultSet{
+			partial := &spannerpb.PartialResultSet{
 				Metadata:    s.ResultSet.Metadata,
 				Values:      values,
 				ResumeToken: rt,
-			})
+			}
+			result = append(result, partial)
 
 			startIndex += rowCount
 			if startIndex == totalRows {
+				partial.Last = true
 				break
 			}
 		}
 	} else {
 		result = append(result, &spannerpb.PartialResultSet{
+			Last:     true,
 			Metadata: s.ResultSet.Metadata,
 		})
 	}
@@ -198,6 +201,7 @@ func (s *StatementResult) updateCountToPartialResultSet(exact bool, resultSetWit
 		Metadata: &spannerpb.ResultSetMetadata{
 			RowType: &spannerpb.StructType{},
 		},
+		Last:  true,
 		Stats: s.convertUpdateCountToResultSet(exact).Stats,
 	}
 	if resultSetWithTx != nil && resultSetWithTx.Metadata != nil && resultSetWithTx.Metadata.Transaction != nil {