[Predator] Make ``CallStackDetector`` return a namedtuple.

appengine/findit/crash/test/stacktrace_test.py

 # Copyright 2016 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.
 
 from common.dependency import Dependency
+from crash.callstack_detectors import StartOfCallStack
 from crash.stacktrace import CallStack
 from crash.stacktrace import CallStackBuffer
 from crash.stacktrace import StackFrame
 from crash.stacktrace import Stacktrace
 from crash.stacktrace import StacktraceBuffer
 from crash.test.stacktrace_test_suite import StacktraceTestSuite
 from crash.type_enums import CallStackFormatType
 from crash.type_enums import LanguageType
 
 
@@ skipping 133 matching lines @@
     expected_callstack = CallStack(stack_buffer.priority,
                                    tuple(frame_list),
                                    CallStackFormatType.DEFAULT,
                                    LanguageType.CPP)
     self.assertTupleEqual(stack_buffer.ToCallStack(), expected_callstack)
 
   def testToCallStackForEmptyCallStackBuffer(self):
     """Tests ``ToCallStack`` for empty  ``CallStackBuffer`` object."""
     self.assertIsNone(CallStackBuffer(0, frame_list=[]).ToCallStack())
 
+  def testFromNoneStartOfCallStack(self):
+    """Tests ``FromStartOfCallStack`` with None input."""
+    self.assertIsNone(CallStackBuffer.FromStartOfCallStack(None))
+
+  def testFromStartOfCallStack(self):
+    """Tests ``FromStartOfCallStack`` with ``StartOfCallStack`` input."""
+    start_of_callstack = StartOfCallStack(0, CallStackFormatType.DEFAULT,
+                                          LanguageType.CPP, {'pid': 123})
+    stack_buffer = CallStackBuffer.FromStartOfCallStack(start_of_callstack)
+    self.assertEqual(stack_buffer.priority, start_of_callstack.priority)
+    self.assertEqual(stack_buffer.format_type, start_of_callstack.format_type)
+    self.assertEqual(stack_buffer.language_type,
+                     start_of_callstack.language_type)
+    self.assertDictEqual(stack_buffer.metadata, start_of_callstack.metadata)
+
 
 class StacktraceTest(StacktraceTestSuite):
 
   def testStacktraceLen(self):
     """Tests ``len`` for ``Stacktrace`` object."""
     frame_list1 = [
         StackFrame(0, 'src/', 'func', 'file0.cc', 'src/file0.cc', [32])]
 
     frame_list2 = [
         StackFrame(0, 'src/', 'func2', 'file0.cc', 'src/file0.cc', [32])]
@@ skipping 115 matching lines @@
 
     stacktrace_buffer = StacktraceBuffer(filters=[_MockKeepFirstFrame])
     stacktrace_buffer.AddFilteredStack(stack_buffer)
     self._VerifyTwoCallStacksEqual(
         stacktrace_buffer.stacks[0],
         CallStackBuffer(stack_buffer.priority, frame_list=frame_list[:1]))
 
   def testEmptyStacktraceBufferToStacktrace(self):
     """Tests that ``ToStacktrace`` returns None for empty stacktrace buffer."""
     self.assertIsNone(StacktraceBuffer([]).ToStacktrace())