Telemetry: Create new profile creator large_profile_creator.

tools/perf/profile_creators/cookie_profile_extender_unittest.py

+# Copyright 2015 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+import os
+import sqlite3
+import tempfile
+import unittest
+
+from profile_creators.cookie_profile_extender import CookieProfileExtender
+
+
+# Testing private method.
+# pylint: disable=protected-access
+class CookieProfileExtenderTest(unittest.TestCase):
+  def _CreateCookieTable(self, path):
+    connection = sqlite3.connect(path)
+    cursor = connection.cursor()
+    cursor.execute("CREATE TABLE cookies (url text)")
+    connection.commit()
+    connection.close()
+
+  def _AddCookiesToTable(self, path, count):
+    connection = sqlite3.connect(path)
+    cursor = connection.cursor()
+    for i in range(count):
+      cursor.execute("INSERT INTO cookies VALUES ('%s')" % i)
+    connection.commit()
+    connection.close()
+
+  def testCookieCount(self):
+    handle, path = tempfile.mkstemp()

[nednguyen, 2015/02/19 00:33:31]

Can you try tempfile.TemporaryFile() here also?

with tempfile.TemporaryFile() as tmp:
 ...

[erikchen, 2015/02/19 01:56:03]

The behavior of TemporaryFile() is OS dependent, and does not make any
guarantees about the actual state of the file system. This unit test requires
actual file system modifications, since it passes around a path of a sql db.

Quoting the python documentation:
"""
your code should not rely on a temporary file created using this function having
or not having a visible name in the file system.
"""

NamedTemporaryFile() doesn't work either.
 "Whether the name can be used to open the file a second time, while the named
temporary file is still open, varies across platforms (it can be so used on
Unix; it cannot on Windows NT or later)"
So we'd have to close the file (with delete=False) for sqlite3 to be able to
access it on Windows, which is exactly the same as mkstemp.

[nednguyen, 2015/02/19 17:07:37]

Thanks for clear explanation. :-)

[sullivan, 2015/02/19 18:24:42]

We've had test breakages before due to platform-specific usage of tempfile APIs.
Maybe it's worth adding a comment why we are using mkstemp?

+    try:
+      os.close(handle)
+
+      self._CreateCookieTable(path)
+      self.assertEquals(CookieProfileExtender._CookieCountInDB(path), 0)
+
+      self._AddCookiesToTable(path, 100)
+      self.assertEquals(CookieProfileExtender._CookieCountInDB(path), 100)
+    finally:
+      os.remove(path)