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 asif and raw; base ISO remains unchanged (content hash and ISO signature).
 - Base image is non-ISO: EnsureDisk converts diffdisk to raw and asif.

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

Author: ashwat287

pkg/driverutil/disk_test.go

@@ -0,0 +1,175 @@
+// SPDX-FileCopyrightText: Copyright The Lima Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package driverutil
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"strconv"
+	"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")
+	typeASIF = image.Type("asif")
+)
+
+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 checkDisk(t *testing.T, diff string, expectedType image.Type) {
+	t.Helper()
+	fi, err := os.Stat(diff)
+	assert.NilError(t, err)
+	assert.Assert(t, fi.Size() > 0)
+	assert.Equal(t, detectImageType(t, diff), expectedType)
+}
+
+func removeAndCheck(t *testing.T, path string) {
+	t.Helper()
+	assert.NilError(t, os.Remove(path))
+	_, err := os.Stat(path)
+	assert.ErrorIs(t, err, os.ErrNotExist)
+}
+
+func isMacOS26OrHigher(t *testing.T) bool {
+	if runtime.GOOS != "darwin" {
+		return false
+	}
+	out, err := exec.CommandContext(t.Context(), "sw_vers", "-productVersion").Output()
+	if err != nil {
+		return false
+	}
+	parts := strings.Split(strings.TrimSpace(string(out)), ".")
+	if len(parts) < 1 {
+		return false
+	}
+	major, err := strconv.Atoi(parts[0])
+	if err != nil {
+		return false
+	}
+	return major >= 26
+}
+
+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)
+
+	formats := []image.Type{typeRAW}
+	if isMacOS26OrHigher(t) {
+		formats = append(formats, typeASIF)
+	}
+
+	for _, format := range formats {
+		assert.NilError(t, EnsureDisk(t.Context(), instDir, "2MiB", format))
+		isISO, err = iso9660util.IsISO9660(base)
+		assert.NilError(t, err)
+		assert.Assert(t, isISO)
+		assert.Equal(t, baseHashBefore, sha256File(t, base))
+		checkDisk(t, diff, format)
+		if format != formats[len(formats)-1] {
+			removeAndCheck(t, diff)
+		}
+	}
+}
+
+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)
+
+	formats := []image.Type{typeRAW}
+	if isMacOS26OrHigher(t) {
+		formats = append(formats, typeASIF)
+	}
+
+	for _, format := range formats {
+		assert.NilError(t, EnsureDisk(t.Context(), instDir, "2MiB", format))
+		checkDisk(t, diff, format)
+		if format != formats[len(formats)-1] {
+			removeAndCheck(t, diff)
+		}
+	}
+}
+
+func TestEnsureDisk_ExistingDiffDisk(t *testing.T) {
+	instDir := makeTempInstanceDir(t)
+	base := filepath.Join(instDir, filenames.BaseDisk)
+	diff := filepath.Join(instDir, filenames.DiffDisk)
+
+	writeNonISO(t, base)
+
+	formats := []image.Type{typeRAW}
+	if isMacOS26OrHigher(t) {
+		formats = append(formats, typeASIF)
+	}
+
+	for _, format := range formats {
+		assert.NilError(t, os.WriteFile(diff, []byte("preexisting"), 0o644))
+		origHash := sha256File(t, diff)
+		assert.NilError(t, EnsureDisk(t.Context(), instDir, "2MiB", format))
+		assert.Equal(t, sha256File(t, diff), origHash)
+		removeAndCheck(t, diff)
+	}
+}