self-update: add basic test for extractToFile

internal/selfupdate/download_test.go

@@ -0,0 +1,44 @@
+package selfupdate
+
+import (
+	"archive/zip"
+	"bytes"
+	"os"
+	"path/filepath"
+	"testing"
+
+	rtest "github.com/restic/restic/internal/test"
+)
+
+func TestExtractToFileZip(t *testing.T) {
+	printf := func(string, ...interface{}) {}
+	dir := t.TempDir()
+
+	ext := "zip"
+	data := []byte("Hello World!")
+
+	// create dummy archive
+	var archive bytes.Buffer
+	zw := zip.NewWriter(&archive)
+	w, err := zw.CreateHeader(&zip.FileHeader{
+		Name:               "example.exe",
+		UncompressedSize64: uint64(len(data)),
+	})
+	rtest.OK(t, err)
+	_, err = w.Write(data[:])
+	rtest.OK(t, err)
+	rtest.OK(t, zw.Close())
+
+	// run twice to test creating a new file and overwriting
+	for i := 0; i < 2; i++ {
+		outfn := filepath.Join(dir, ext+"-out")
+		rtest.OK(t, extractToFile(archive.Bytes(), "src."+ext, outfn, printf))
+
+		outdata, err := os.ReadFile(outfn)
+		rtest.OK(t, err)
+		rtest.Assert(t, bytes.Equal(data[:], outdata), "%v contains wrong data", outfn)
+
+		// overwrite to test the file is properly overwritten
+		rtest.OK(t, os.WriteFile(outfn, []byte{1, 2, 3}, 0))
+	}
+}