Begin breaking apart gam.py into logical pieces

.travis.yml

@@ -198,6 +198,8 @@ install:
 - source src/travis/$TRAVIS_OS_NAME-$PLATFORM-install.sh
 
 script:
+# Discover and run all Python unit tests
+- $python -m unittest discover -s ./ -p "*_test.py"
 - $gam version extended
 - $gam version | grep travis # travis should be part of the path (not /tmp or such)
 # determine which Python version GAM is built with and ensure it's at least build version from above.

src/controlflow.py

@@ -0,0 +1,66 @@
+"""Methods related to the central control flow of an application."""
+import random
+import sys
+import time
+
+import display  # TODO: Change to relative import when gam is setup as a package
+from var import MESSAGE_HEADER_NOT_FOUND_IN_CSV_HEADERS
+from var import MESSAGE_INVALID_JSON
+
+
+def system_error_exit(return_code, message):
+  """Raises a system exit with the given return code and message.
+
+  Args:
+    return_code: Int, the return code to yield when the system exits.
+    message: An error message to print before the system exits.
+  """
+  if message:
+    display.print_error(message)
+  sys.exit(return_code)
+
+
+def csv_field_error_exit(field_name, field_names):
+  """Raises a system exit when a CSV field is malformed.
+
+  Args:
+    field_name: The CSV field name for which a header does not exist in the
+      existing CSV headers.
+    field_names: The known list of CSV headers.
+  """
+  system_error_exit(
+      2,
+      MESSAGE_HEADER_NOT_FOUND_IN_CSV_HEADERS.format(field_name,
+                                                     ','.join(field_names)))
+
+
+def invalid_json_exit(file_name):
+  """Raises a sysyem exit when invalid JSON content is encountered."""
+  system_error_exit(17, MESSAGE_INVALID_JSON.format(file_name))
+
+
+def wait_on_failure(current_attempt_num,
+                    total_num_retries,
+                    error_message,
+                    error_print_threshold=3):
+  """Executes an exponential backoff-style system sleep.
+
+  Args:
+    current_attempt_num: Int, the current number of retries.
+    total_num_retries: Int, the total number of times the current action will be
+      retried.
+    error_message: String, a message to be displayed that will give more context
+      around why the action is being retried.
+    error_print_threshold: Int, the number of attempts which will have their
+      error messages suppressed. Any current_attempt_num greater than
+      error_print_threshold will print the prescribed error.
+  """
+  wait_on_fail = min(2**current_attempt_num,
+                     60) + float(random.randint(1, 1000)) / 1000
+  if current_attempt_num > error_print_threshold:
+    sys.stderr.write(
+        'Temporary error: {0}, Backing off: {1} seconds, Retry: {2}/{3}\n'
+        .format(error_message, int(wait_on_fail), current_attempt_num,
+                total_num_retries))
+    sys.stderr.flush()
+  time.sleep(wait_on_fail)

src/controlflow_test.py

@@ -0,0 +1,108 @@
+"""Tests for controlflow."""
+
+import unittest
+from unittest.mock import patch
+
+import controlflow
+
+
+class ControlFlowTest(unittest.TestCase):
+
+  def test_system_error_exit_raises_systemexit_error(self):
+    with self.assertRaises(SystemExit):
+      controlflow.system_error_exit(1, 'exit message')
+
+  def test_system_error_exit_raises_systemexit_with_return_code(self):
+    with self.assertRaises(SystemExit) as context_manager:
+      controlflow.system_error_exit(100, 'exit message')
+    self.assertEqual(context_manager.exception.code, 100)
+
+  @patch.object(controlflow.display, 'print_error')
+  def test_system_error_exit_prints_error_before_exiting(self, mock_print_err):
+    with self.assertRaises(SystemExit):
+      controlflow.system_error_exit(100, 'exit message')
+    self.assertIn('exit message', mock_print_err.call_args[0][0])
+
+  def test_csv_field_error_exit_raises_systemexit_error(self):
+    with self.assertRaises(SystemExit):
+      controlflow.csv_field_error_exit('aField',
+                                       ['unusedField1', 'unusedField2'])
+
+  def test_csv_field_error_exit_exits_code_2(self):
+    with self.assertRaises(SystemExit) as context_manager:
+      controlflow.csv_field_error_exit('aField',
+                                       ['unusedField1', 'unusedField2'])
+    self.assertEqual(context_manager.exception.code, 2)
+
+  @patch.object(controlflow.display, 'print_error')
+  def test_csv_field_error_exit_prints_error_details(self, mock_print_err):
+    with self.assertRaises(SystemExit):
+      controlflow.csv_field_error_exit('aField',
+                                       ['unusedField1', 'unusedField2'])
+    printed_message = mock_print_err.call_args[0][0]
+    self.assertIn('aField', printed_message)
+    self.assertIn('unusedField1', printed_message)
+    self.assertIn('unusedField2', printed_message)
+
+  def test_invalid_json_exit_raises_systemexit_error(self):
+    with self.assertRaises(SystemExit):
+      controlflow.invalid_json_exit('filename')
+
+  def test_invalid_json_exit_exit_exits_code_17(self):
+    with self.assertRaises(SystemExit) as context_manager:
+      controlflow.invalid_json_exit('filename')
+    self.assertEqual(context_manager.exception.code, 17)
+
+  @patch.object(controlflow.display, 'print_error')
+  def test_invalid_json_exit_prints_error_details(self, mock_print_err):
+    with self.assertRaises(SystemExit):
+      controlflow.invalid_json_exit('filename')
+    printed_message = mock_print_err.call_args[0][0]
+    self.assertIn('filename', printed_message)
+
+  @patch.object(controlflow.time, 'sleep')
+  def test_wait_on_failure_waits_exponentially(self, mock_sleep):
+    controlflow.wait_on_failure(1, 5, 'Backoff attempt #1')
+    controlflow.wait_on_failure(2, 5, 'Backoff attempt #2')
+    controlflow.wait_on_failure(3, 5, 'Backoff attempt #3')
+
+    sleep_calls = mock_sleep.call_args_list
+    self.assertGreaterEqual(sleep_calls[0][0][0], 2**1)
+    self.assertGreaterEqual(sleep_calls[1][0][0], 2**2)
+    self.assertGreaterEqual(sleep_calls[2][0][0], 2**3)
+
+  @patch.object(controlflow.time, 'sleep')
+  def test_wait_on_failure_does_not_exceed_60_secs_wait(self, mock_sleep):
+    total_attempts = 20
+    for attempt in range(1, total_attempts + 1):
+      controlflow.wait_on_failure(
+          attempt,
+          total_attempts,
+          'Attempt #%s' % attempt,
+          # Suppress messages while we make a lot of attempts.
+          error_print_threshold=total_attempts + 1)
+      # Wait time may be between 60 and 61 secs, due to rand addition.
+      self.assertLess(mock_sleep.call_args[0][0], 61)
+
+  # Prevent the system from actually sleeping and thus slowing down the test.
+  @patch.object(controlflow.time, 'sleep')
+  @patch.object(controlflow.sys.stderr, 'write')
+  def test_wait_on_failure_prints_errors(self, mock_stderr_write,
+                                         unused_mock_sleep):
+    message = 'An error message to display'
+    controlflow.wait_on_failure(1, 5, message, error_print_threshold=0)
+    self.assertIn(message, mock_stderr_write.call_args[0][0])
+
+  @patch.object(controlflow.time, 'sleep')
+  @patch.object(controlflow.sys.stderr, 'write')
+  def test_wait_on_failure_only_prints_after_threshold(self, mock_stderr_write,
+                                                       unused_mock_sleep):
+    total_attempts = 5
+    threshold = 3
+    for attempt in range(1, total_attempts + 1):
+      controlflow.wait_on_failure(
+          attempt,
+          total_attempts,
+          'Attempt #%s' % attempt,
+          error_print_threshold=threshold)
+    self.assertEqual(total_attempts - threshold, mock_stderr_write.call_count)

src/display.py

@@ -0,0 +1,18 @@
+"""Methods related to display of information to the user."""
+
+import sys
+import utils
+from var import ERROR_PREFIX
+from var import WARNING_PREFIX
+
+
+def print_error(message):
+  """Prints a one-line error message to stderr in a standard format."""
+  sys.stderr.write(
+      utils.convertUTF8('\n{0}{1}\n'.format(ERROR_PREFIX, message)))
+
+
+def print_warning(message):
+  """Prints a one-line warning message to stderr in a standard format."""
+  sys.stderr.write(
+      utils.convertUTF8('\n{0}{1}\n'.format(WARNING_PREFIX, message)))

src/display_test.py

@@ -0,0 +1,59 @@
+"""Tests for display."""
+
+import unittest
+from unittest.mock import patch
+
+import display
+from var import ERROR_PREFIX
+from var import WARNING_PREFIX
+
+
+class DisplayTest(unittest.TestCase):
+
+  @patch.object(display.sys.stderr, 'write')
+  def test_print_error_prints_to_stderr(self, mock_write):
+    message = 'test error'
+    display.print_error(message)
+    printed_message = mock_write.call_args[0][0]
+    self.assertIn(message, printed_message)
+
+  @patch.object(display.sys.stderr, 'write')
+  def test_print_error_prints_error_prefix(self, mock_write):
+    message = 'test error'
+    display.print_error(message)
+    printed_message = mock_write.call_args[0][0]
+    self.assertLess(
+        printed_message.find(ERROR_PREFIX), printed_message.find(message),
+        'The error prefix does not appear before the error message')
+
+  @patch.object(display.sys.stderr, 'write')
+  def test_print_error_ends_message_with_newline(self, mock_write):
+    message = 'test error'
+    display.print_error(message)
+    printed_message = mock_write.call_args[0][0]
+    self.assertRegex(printed_message, '\n$',
+                     'The error message does not end in a newline.')
+
+  @patch.object(display.sys.stderr, 'write')
+  def test_print_warning_prints_to_stderr(self, mock_write):
+    message = 'test warning'
+    display.print_warning(message)
+    printed_message = mock_write.call_args[0][0]
+    self.assertIn(message, printed_message)
+
+  @patch.object(display.sys.stderr, 'write')
+  def test_print_warning_prints_error_prefix(self, mock_write):
+    message = 'test warning'
+    display.print_error(message)
+    printed_message = mock_write.call_args[0][0]
+    self.assertLess(
+        printed_message.find(WARNING_PREFIX), printed_message.find(message),
+        'The warning prefix does not appear before the error message')
+
+  @patch.object(display.sys.stderr, 'write')
+  def test_print_warning_ends_message_with_newline(self, mock_write):
+    message = 'test warning'
+    display.print_error(message)
+    printed_message = mock_write.call_args[0][0]
+    self.assertRegex(printed_message, '\n$',
+                     'The warning message does not end in a newline.')