make test more reliable and faster

driver_test.go

@@ -2946,8 +2946,8 @@ func TestValuerWithValueReceiverGivenNilValue(t *testing.T) {
 // call to `Rows.Close`, so Context cancellation should **not** invalidate the backing buffers.
 func TestRawBytesAreNotModified(t *testing.T) {
 	const blob = "abcdefghijklmnop"
-	const contextRaceIterations = 10
-	const blobSize = 3000
+	const contextRaceIterations = 20
+	const blobSize = defaultBufSize * 3 / 4  // Second row overwrites first row.
 	const insertRows = 4
 
 	var sqlBlobs = [2]string{
@@ -2981,11 +2981,11 @@ func TestRawBytesAreNotModified(t *testing.T) {
 					before := string(raw)
 					// Ensure cancelling the query does not corrupt the contents of `raw`
 					cancel()
-					time.Sleep(5 * time.Millisecond)
+					time.Sleep(time.Microsecond * 100)
 					after := string(raw)
 
 					if before != after {
-						t.Fatal("the backing storage for sql.RawBytes has been modified")
+						t.Fatalf("the backing storage for sql.RawBytes has been modified (i=%v)", i)
 					}
 				}
 				rows.Close()