stats_manager: prepare StatsManager to be a utility used in hdctools

This is the first CL in a series of CLs to start using StatsManager in
servo/hdctools (package depends on ec-devutils, as in this package).
This CL:
- beefs up StatsManager to handle unavailable units more gracefully
- adds a few more tests to stats_manager_unittest.py
- adds some minor unit testing for powerlog's file retrieval logic

BRANCH=None
BUG=chromium:760267
TEST=manual testing, unit tests still pass, powerlog still works

Change-Id: Ifcdfcc482008484fbc21326c6f087ebf466c3e74
Signed-off-by: Ruben Rodriguez Buchillon <coconutruben@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1140025
Reviewed-by: Mengqi Guo <mqg@chromium.org>

1 files changed, 49 insertions, 0 deletions

diff --git a/extra/usb_power/powerlog_unittest.py b/extra/usb_power/powerlog_unittest.py
new file mode 100644
index 0000000000..7058c57aa7
--- /dev/null
+++ b/extra/usb_power/powerlog_unittest.py
@@ -0,0 +1,49 @@
+# Copyright 2018 The Chromium OS Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+"""Unit tests for powerlog."""
+
+import os
+import shutil
+import tempfile
+import unittest
+
+import powerlog
+
+class TestPowerlog(unittest.TestCase):
+  """Test to verify powerlog util methods work as expected."""
+
+  def setUp(self):
+    """Set up data and create a temporary directory to save data and stats."""
+    self.tempdir = tempfile.mkdtemp()
+    self.filename = 'testfile'
+    self.filepath = os.path.join(self.tempdir, self.filename)
+    with open(self.filepath, 'w') as f:
+      f.write('')
+
+  def tearDown(self):
+    """Delete the temporary directory and its content."""
+    shutil.rmtree(self.tempdir)
+
+  def test_ProcessFilenameAbsoluteFilePath(self):
+    """Absolute file path is returned unchanged."""
+    processed_fname = powerlog.process_filename(self.filepath)
+    self.assertEqual(self.filepath, processed_fname)
+
+  def test_ProcessFilenameRelativeFilePath(self):
+    """Finds relative file path inside a known config location."""
+    original = powerlog.CONFIG_LOCATIONS
+    powerlog.CONFIG_LOCATIONS = [self.tempdir]
+    processed_fname = powerlog.process_filename(self.filename)
+    try:
+      self.assertEqual(self.filepath, processed_fname)
+    finally:
+      powerlog.CONFIG_LOCATIONS = original
+
+  def test_ProcessFilenameInvalid(self):
+    """IOError is raised when file cannot be found by any of the four ways."""
+    with self.assertRaises(IOError):
+      powerlog.process_filename(self.filename)
+
+if __name__ == '__main__':
+  unittest.main()