rbd: add validation to ToCSI() for rbdVolume and rbdSnapshot

After an unfortnate timed restart of the provisioner, a volume that got
cloned did not get a `rbdVolume.VolID` set. The `.VolID` is used as the
CSI Volume Handle, and is a required attribute.

The `rbdVolume` and `rbdSnapshot` structs have a `.ToCSI()` function
that can do the validation of required attributes. This is now added,
including unit-tests.

Signed-off-by: Niels de Vos <ndevos@ibm.com>

internal/rbd/snapshot_test.go

@@ -0,0 +1,86 @@
+/*
+Copyright 2025 The Ceph-CSI Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package rbd
+
+import (
+	"context"
+	"testing"
+	"time"
+)
+
+func TestToCSISnapshot(t *testing.T) {
+	t.Parallel()
+	now := time.Now()
+	tests := []struct {
+		name    string
+		rs      *rbdSnapshot
+		wantErr bool
+	}{
+		{
+			name: "all attributes set",
+			rs: &rbdSnapshot{
+				rbdImage: rbdImage{
+					VolID:     "0001-unique-snapshot-id",
+					CreatedAt: &now,
+				},
+				SourceVolumeID: "0001-unique-volume-id",
+			},
+			wantErr: false,
+		},
+		{
+			name: "missing volume-id",
+			rs: &rbdSnapshot{
+				rbdImage: rbdImage{
+					VolID:     "",
+					CreatedAt: &now,
+				},
+				SourceVolumeID: "0001-unique-volume-id",
+			},
+			wantErr: true,
+		},
+		{
+			name: "missing source-volume-id",
+			rs: &rbdSnapshot{
+				rbdImage: rbdImage{
+					VolID:     "0001-unique-snapshot-id",
+					CreatedAt: &now,
+				},
+				SourceVolumeID: "",
+			},
+			wantErr: true,
+		},
+		{
+			name: "missing creation-time",
+			rs: &rbdSnapshot{
+				rbdImage: rbdImage{
+					VolID:     "0001-unique-snapshot-id",
+					CreatedAt: nil,
+				},
+				SourceVolumeID: "0001-unique-volume-id",
+			},
+			wantErr: true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			if _, err := tt.rs.ToCSI(context.TODO()); (err != nil) != tt.wantErr {
+				t.Errorf("ToCSI() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}