[recipe_modules/file] add real file module to engine.

recipe_modules/file/examples/copy.py

+# 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.
+
+DEPS = [
+  "file",
+  "path",
+]
+
+
+def RunSteps(api):
+  dest = api.path['start_dir'].join('some file')
+  data = 'Here is some text data'
+
+  api.file.write_text('write a file', dest, data)
+  api.file.copy('copy it', dest, api.path['start_dir'].join('new path'))
+  read_data = api.file.read_text(
+    'read it', api.path['start_dir'].join('new path'), test_data=data)
+
+  assert read_data == data, (read_data, data)
+
+  api.file.move('move it', api.path['start_dir'].join('new path'),
+                api.path['start_dir'].join('new new path'))
+
+  read_data = api.file.read_text(
+    'read it', api.path['start_dir'].join('new new path'), test_data=data)
+
+  assert read_data == data, (read_data, data)
+
+
+def GenTests(api):
+  yield api.test('basic')