move rootfstest to tartest

it's not "rootfs" or "docker" any more.

internal/tartest/BUILD

@@ -0,0 +1,16 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["tartest.go"],
+    importpath = "github.com/motiejus/code/undocker/internal/tartest",
+    visibility = ["//visibility:public"],
+    deps = ["@com_github_stretchr_testify//require:go_default_library"],
+)
+
+go_test(
+    name = "go_default_test",
+    srcs = ["tartest_test.go"],
+    embed = [":go_default_library"],
+    deps = ["@com_github_stretchr_testify//assert:go_default_library"],
+)

internal/tartest/tartest.go

@@ -0,0 +1,119 @@
+package tartest
+
+import (
+	"archive/tar"
+	"bytes"
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+type (
+	Tarrer interface {
+		Tar(*tar.Writer) error
+	}
+
+	Tarball []Tarrer
+
+	// Extractable is an empty interface for comparing extracted outputs in tests.
+	// Using that just to avoid the ugly `interface{}`.
+	Extractable interface{}
+
+	Dir struct {
+		Name string
+		Uid  int
+	}
+
+	File struct {
+		Name     string
+		Uid      int
+		Contents *bytes.Buffer
+	}
+
+	Hardlink struct {
+		Name string
+		Uid  int
+	}
+)
+
+func (tb Tarball) Buffer() *bytes.Buffer {
+	var buf bytes.Buffer
+	tw := tar.NewWriter(&buf)
+	for _, member := range tb {
+		member.Tar(tw)
+	}
+	tw.Close()
+	return &buf
+}
+
+func (d Dir) Tar(tw *tar.Writer) error {
+	hdr := &tar.Header{
+		Typeflag: tar.TypeDir,
+		Name:     d.Name,
+		Mode:     0644,
+		Uid:      d.Uid,
+	}
+	return tw.WriteHeader(hdr)
+}
+
+func (f File) Tar(tw *tar.Writer) error {
+	var contents []byte
+	if f.Contents != nil {
+		contents = f.Contents.Bytes()
+	}
+	hdr := &tar.Header{
+		Typeflag: tar.TypeReg,
+		Name:     f.Name,
+		Mode:     0644,
+		Uid:      f.Uid,
+		Size:     int64(len(contents)),
+	}
+	if err := tw.WriteHeader(hdr); err != nil {
+		return err
+	}
+	if _, err := tw.Write(contents); err != nil {
+		return err
+	}
+	return nil
+}
+
+func (h Hardlink) Tar(tw *tar.Writer) error {
+	return tw.WriteHeader(&tar.Header{
+		Typeflag: tar.TypeLink,
+		Name:     h.Name,
+		Mode:     0644,
+		Uid:      h.Uid,
+	})
+}
+
+func Extract(t *testing.T, r io.Reader) []Extractable {
+	t.Helper()
+	ret := []Extractable{}
+	tr := tar.NewReader(r)
+	for {
+		hdr, err := tr.Next()
+		if err == io.EOF {
+			break
+		}
+		require.NoError(t, err)
+
+		var elem Extractable
+		switch hdr.Typeflag {
+		case tar.TypeDir:
+			elem = Dir{Name: hdr.Name, Uid: hdr.Uid}
+		case tar.TypeLink:
+			elem = Hardlink{Name: hdr.Name}
+		case tar.TypeReg:
+			f := File{Name: hdr.Name, Uid: hdr.Uid}
+			if hdr.Size > 0 {
+				var buf bytes.Buffer
+				io.Copy(&buf, tr)
+				f.Contents = &buf
+			}
+			elem = f
+		}
+		ret = append(ret, elem)
+	}
+	return ret
+}

internal/tartest/tartest_test.go

@@ -0,0 +1,28 @@
+package tartest
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestTarball(t *testing.T) {
+	bk := Tarball{File{Name: "entrypoint.sh", Contents: bytes.NewBufferString("hello")}}
+	img := Tarball{
+		File{Name: "backup.tar", Contents: bk.Buffer()},
+		File{Name: "entrypoint.sh", Contents: bytes.NewBufferString("bye")},
+		Dir{Name: "bin"},
+		Hardlink{Name: "entrypoint2"},
+	}
+
+	got := Extract(t, img.Buffer())
+	want := []Extractable{
+		File{Name: "backup.tar", Contents: bk.Buffer()},
+		File{Name: "entrypoint.sh", Contents: bytes.NewBufferString("bye")},
+		Dir{Name: "bin"},
+		Hardlink{Name: "entrypoint2"},
+	}
+
+	assert.Equal(t, want, got)
+}