test(driverutil): add EnsureDisk tests for ISO and non-ISO base images

Add pkg/driverutil/disk_test.go covering:
 - Base image is ISO: EnsureDisk creates/keeps diffdisk and converts to raw; base ISO remains unchanged (content hash and ISO signature).
 - Base image is non-ISO: EnsureDisk converts diffdisk to raw.

Signed-off-by: ashwat287 <ashwatpas@gmail.com>

Author: ashwat287

pkg/driverutil/disk_test.go

@@ -0,0 +1,118 @@
+// SPDX-FileCopyrightText: Copyright The Lima Authors
+// SPDX-License-Identifier: Apache-2.0
+package driverutil
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/lima-vm/go-qcow2reader"
+	"github.com/lima-vm/go-qcow2reader/image"
+	"gotest.tools/v3/assert"
+
+	"github.com/lima-vm/lima/v2/pkg/iso9660util"
+	"github.com/lima-vm/lima/v2/pkg/limatype/filenames"
+)
+
+const typeRAW = image.Type("raw")
+
+func makeTempInstanceDir(t *testing.T) string {
+	t.Helper()
+	return t.TempDir()
+}
+
+func writeMinimalISO(t *testing.T, path string) {
+	t.Helper()
+	entries := []iso9660util.Entry{
+		{Path: "/hello.txt", Reader: strings.NewReader("hello world")},
+	}
+	assert.NilError(t, iso9660util.Write(path, "TESTISO", entries))
+}
+
+func writeNonISO(t *testing.T, path string) {
+	t.Helper()
+	size := 64 * 1024
+	buf := make([]byte, size)
+	copy(buf[0x8001:], "XXXXX")
+	assert.NilError(t, os.WriteFile(path, buf, 0o644))
+}
+
+func sha256File(t *testing.T, path string) string {
+	t.Helper()
+	b, err := os.ReadFile(path)
+	assert.NilError(t, err)
+	sum := sha256.Sum256(b)
+	return hex.EncodeToString(sum[:])
+}
+
+func detectImageType(t *testing.T, path string) image.Type {
+	t.Helper()
+	f, err := os.Open(path)
+	assert.NilError(t, err)
+	defer f.Close()
+	img, err := qcow2reader.Open(f)
+	assert.NilError(t, err)
+	return img.Type()
+}
+
+func TestEnsureDisk_WithISOBaseImage(t *testing.T) {
+	instDir := makeTempInstanceDir(t)
+	base := filepath.Join(instDir, filenames.BaseDisk)
+	diff := filepath.Join(instDir, filenames.DiffDisk)
+
+	writeMinimalISO(t, base)
+
+	isISO, err := iso9660util.IsISO9660(base)
+	assert.NilError(t, err)
+	assert.Assert(t, isISO)
+	baseHashBefore := sha256File(t, base)
+
+	assert.NilError(t, EnsureDisk(t.Context(), instDir, "2MiB", typeRAW))
+
+	isISO, err = iso9660util.IsISO9660(base)
+	assert.NilError(t, err)
+	assert.Assert(t, isISO)
+	assert.Equal(t, baseHashBefore, sha256File(t, base))
+
+	fi, err := os.Stat(diff)
+	assert.NilError(t, err)
+	assert.Assert(t, fi.Size() > 0)
+	assert.Equal(t, detectImageType(t, diff), typeRAW)
+}
+
+func TestEnsureDisk_WithNonISOBaseImage(t *testing.T) {
+	instDir := makeTempInstanceDir(t)
+	base := filepath.Join(instDir, filenames.BaseDisk)
+	diff := filepath.Join(instDir, filenames.DiffDisk)
+
+	writeNonISO(t, base)
+
+	isISO, err := iso9660util.IsISO9660(base)
+	assert.NilError(t, err)
+	assert.Assert(t, !isISO)
+
+	assert.NilError(t, EnsureDisk(t.Context(), instDir, "2MiB", typeRAW))
+
+	fi, err := os.Stat(diff)
+	assert.NilError(t, err)
+	assert.Assert(t, fi.Size() > 0)
+	assert.Equal(t, detectImageType(t, diff), typeRAW)
+}
+
+func TestEnsureDisk_ExistingDiffDisk(t *testing.T) {
+	instDir := makeTempInstanceDir(t)
+	base := filepath.Join(instDir, filenames.BaseDisk)
+	diff := filepath.Join(instDir, filenames.DiffDisk)
+
+	writeNonISO(t, base)
+	assert.NilError(t, os.WriteFile(diff, []byte("preexisting"), 0o644))
+	origHash := sha256File(t, diff)
+
+	assert.NilError(t, EnsureDisk(t.Context(), instDir, "2MiB", typeRAW))
+
+	assert.Equal(t, sha256File(t, diff), origHash)
+}