stages/disks: Add some partitioning unit tests

Signed-off-by: James Le Cuirot <jlecuirot@microsoft.com>

Author: chewi

internal/exec/stages/disks/partitions_test.go

@@ -0,0 +1,67 @@
+// Copyright 2025 CoreOS, Inc.
+//
+// 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 disks
+
+import (
+	"testing"
+)
+
+func TestPartitionNumberPrefix(t *testing.T) {
+	tests := []struct {
+		in  string
+		out string
+	}{
+		{"/dev/sda", ""},
+		{"/dev/vda", ""},
+		{"/dev/nvme0n1", "p"},
+		{"/dev/mmcblk0", "p"},
+		{"/dev/loop0", "p"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.in, func(t *testing.T) {
+			got := partitionNumberPrefix(tt.in)
+			if got != tt.out {
+				t.Errorf("partitionNumberPrefix(%q) = %q, want %q", tt.in, got, tt.out)
+			}
+		})
+	}
+}
+
+func TestPartitionDevPath(t *testing.T) {
+	tests := []struct {
+		blockDev string
+		dmName   string
+		prefix   string
+		partNum  int
+		out      string
+	}{
+		{"/dev/sda", "", "", 1, "/dev/sda1"},
+		{"/dev/sda", "", "", 12, "/dev/sda12"},
+		{"/dev/nvme0n1", "", "p", 1, "/dev/nvme0n1p1"},
+		{"/dev/nvme0n1", "", "p", 3, "/dev/nvme0n1p3"},
+		{"/dev/mmcblk0", "", "p", 2, "/dev/mmcblk0p2"},
+		{"/dev/dm-0", "mpath0", "p", 1, "/dev/disk/by-id/dm-name-mpath0p1"},
+		{"/dev/dm-0", "mpath0", "p", 5, "/dev/disk/by-id/dm-name-mpath0p5"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.out, func(t *testing.T) {
+			got := partitionDevPath(tt.blockDev, tt.dmName, tt.prefix, tt.partNum)
+			if got != tt.out {
+				t.Errorf("partitionDevPath(%q, %q, %q, %d) = %q, want %q",
+					tt.blockDev, tt.dmName, tt.prefix, tt.partNum, got, tt.out)
+			}
+		})
+	}
+}