vpython: Add filesystem operation / test packages.

vpython/filesystem/testfs/build.go

Index: vpython/filesystem/testfs/build.go
diff --git a/vpython/filesystem/testfs/build.go b/vpython/filesystem/testfs/build.go
new file mode 100644
index 0000000000000000000000000000000000000000..facf2720ef77408d6d73c342e71dd6f9d2ba657d
--- /dev/null
+++ b/vpython/filesystem/testfs/build.go
@@ -0,0 +1,55 @@
+// Copyright 2017 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package testfs
+
+import (
+	"io/ioutil"
+	"path/filepath"
+	"sort"
+	"strings"
+
+	"github.com/luci/luci-go/vpython/filesystem"
+)
+
+// Build constructs a filesystem hierarchy given a layout.
+//
+// The layouts keys should be ToSlash-style file paths. Its values should be the
+// content that is written at those paths. Intermediate directories will be
+// automatically created.
+//
+// To create a directory, end its path with a "/". In this case, the content
+// will be ignored.
+func Build(base string, layout map[string]string) error {
+	keys := make([]string, 0, len(layout))
+	for k := range layout {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+
+	for _, path := range keys {
+		makeDir := strings.HasSuffix(path, "/")
+		content := layout[path]
+
+		// Normalize "path" to the current OS.
+		path = filepath.Join(base, filepath.FromSlash(path))
+
+		if makeDir {
+			// Make a directory.
+			if err := filesystem.MakeDirs(path); err != nil {
+				return err
+			}
+		} else {
+			// Make a file.
+
+			if err := filesystem.MakeDirs(filepath.Dir(path)); err != nil {
+				return err
+			}
+			if err := ioutil.WriteFile(path, []byte(content), 0644); err != nil {
+				return err
+			}
+		}
+	}
+	return nil
+}