Refactor into Python package format (#1165)

* Refactor into a python module format

-Updates import statements to be absolute vs implicitly relative
-Uses import syntax that minimizes the need to update references in code
and/or reformat affected lines (e.g. `import gapi.directory` becomes `from gam.gapi import directory as
gapi_directory`)
-Adds a `__main__.py` such that the module can be executed on its own
using standard `python3 -m gam` syntax
-Replaces __main__ import hack with module import
-Updates the GAM path to be the module's parent dir

* Add gam.py to /src for backwards compatibility

A stub that calls gam.__main__.main() to be used by users who are not
with the syntax of calling a module implementation. It should also
provide immediate backwards-compatibility with existing scripts with
references to this file.

* Move build tools back to the main dir and out of the package

* Fix pylint errors

* Update build spec to use new package format

Incorporates @jay0lee's patch from
https://github.com/jay0lee/GAM/pull/1165#issuecomment-618430828

src/gam/controlflow_test.py

@@ -0,0 +1,106 @@
+"""Tests for controlflow."""
+
+import unittest
+from unittest.mock import patch
+
+from gam 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.assertLessEqual(mock_sleep.call_args[0][0], 61)
+
+  # Prevent the system from actually sleeping and thus slowing down the test.
+  @patch.object(controlflow.time, 'sleep')
+  def test_wait_on_failure_prints_errors(self, unused_mock_sleep):
+    message = 'An error message to display'
+    with patch.object(controlflow.sys.stderr, 'write') as mock_stderr_write:
+      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')
+  def test_wait_on_failure_only_prints_after_threshold(self, unused_mock_sleep):
+    total_attempts = 5
+    threshold = 3
+    with patch.object(controlflow.sys.stderr, 'write') as mock_stderr_write:
+      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)