Update prebuilt.py to handle files not existing. Add a unittest to test the case

TBR=sosa

BUG=NA
TEST=Unittest

Review URL: http://codereview.chromium.org/6261013

prebuilt.py

@@ -92,7 +92,10 @@ def UpdateLocalFile(filename, value, key='PORTAGE_BINHOST'):
     value: Value to write with the key.
     key: The variable key to update. (Default: PORTAGE_BINHOST)
   """
-  file_fh = open(filename)
+  if os.path.exists(filename):
+    file_fh = open(filename)
+  else:
+    file_fh = open(filename, 'w+')
   file_lines = []
   found = False
   keyval_str = '%(key)s=%(value)s'

prebuilt_unittest.py

@@ -45,9 +45,12 @@ class TestUpdateFile(unittest.TestCase):
   def tearDown(self):
     os.remove(self.version_file)
 
-  def _read_version_file(self):
+  def _read_version_file(self, version_file=None):
     """Read the contents of self.version_file and return as a list."""
-    version_fh = open(self.version_file)
+    if not version_file:
+      version_file = self.version_file
+
+    version_fh = open(version_file)
     try:
       return [line.strip() for line in version_fh.readlines()]
     finally:
@@ -86,6 +89,18 @@ class TestUpdateFile(unittest.TestCase):
     prebuilt.UpdateLocalFile(self.version_file, new_val)
     self._verify_key_pair(key, new_val)
 
+  def testUpdateNonExistentFile(self):
+    key = 'PORTAGE_BINHOST'
+    value = '1234567'
+    non_existent_file = tempfile.mktemp()
+    try:
+      prebuilt.UpdateLocalFile(non_existent_file, value)
+      file_contents = self._read_version_file(non_existent_file)
+      self.assertEqual(file_contents, ['%s=%s' % (key, value)])
+    finally:
+      if os.path.exists(non_existent_file):
+        os.remove(non_existent_file)
+
 
 class TestPrebuiltFilters(unittest.TestCase):