Handling condition where Entity.cause is not a dict. (aws#267)

* Handling condition where cause is not a dict. Exceptions should be appended not replaced.

* Adding more test cases

* Minor fixes to some tests

* Some type checking in python2 may require to import unicode literals

* Checking python version for type comparison

aws_xray_sdk/core/models/entity.py

@@ -211,7 +211,7 @@ def add_exception(self, exception, stack, remote=False):
         """
         Add an exception to trace entities.
 
-        :param Exception exception: the catched exception.
+        :param Exception exception: the caught exception.
         :param list stack: the output from python built-in
             `traceback.extract_stack()`.
         :param bool remote: If False it means it's a client error
@@ -224,7 +224,16 @@ def add_exception(self, exception, stack, remote=False):
             setattr(self, 'cause', getattr(exception, '_cause_id'))
             return
 
-        exceptions = []
+        if not isinstance(self.cause, dict):
+            log.warning("The current cause object is not a dict but an id: {}. Resetting the cause and recording the "
+                        "current exception".format(self.cause))
+            self.cause = {}
+
+        if 'exceptions' in self.cause:
+            exceptions = self.cause['exceptions']
+        else:
+            exceptions = []
+
         exceptions.append(Throwable(exception, stack, remote))
 
         self.cause['exceptions'] = exceptions

tests/test_trace_entities.py

@@ -1,5 +1,7 @@
 # -*- coding: iso-8859-15 -*-
+
 import pytest
+import sys
 
 from aws_xray_sdk.core.models.segment import Segment
 from aws_xray_sdk.core.models.subsegment import Subsegment
@@ -194,3 +196,70 @@ def test_missing_parent_segment():
 
     with pytest.raises(SegmentNotFoundException):
         Subsegment('name', 'local', None)
+
+
+def test_add_exception():
+    segment = Segment('seg')
+    exception = Exception("testException")
+    stack = [['path', 'line', 'label']]
+    segment.add_exception(exception=exception, stack=stack)
+    segment.close()
+
+    cause = segment.cause
+    assert 'exceptions' in cause
+    exceptions = cause['exceptions']
+    assert len(exceptions) == 1
+    assert 'working_directory' in cause
+    exception = exceptions[0]
+    assert 'testException' == exception.message
+    expected_stack = [{'path': 'path', 'line': 'line', 'label': 'label'}]
+    assert expected_stack == exception.stack
+
+
+def test_add_exception_referencing():
+    segment = Segment('seg')
+    subseg = Subsegment('subseg', 'remote', segment)
+    exception = Exception("testException")
+    stack = [['path', 'line', 'label']]
+    subseg.add_exception(exception=exception, stack=stack)
+    segment.add_exception(exception=exception, stack=stack)
+    subseg.close()
+    segment.close()
+
+    seg_cause = segment.cause
+    subseg_cause = subseg.cause
+
+    assert isinstance(subseg_cause, dict)
+    if sys.version_info.major == 2:
+        assert isinstance(seg_cause, basestring)
+    else:
+        assert isinstance(seg_cause, str)
+    assert seg_cause == subseg_cause['exceptions'][0].id
+
+
+def test_add_exception_cause_resetting():
+    segment = Segment('seg')
+    subseg = Subsegment('subseg', 'remote', segment)
+    exception = Exception("testException")
+    stack = [['path', 'line', 'label']]
+    subseg.add_exception(exception=exception, stack=stack)
+    segment.add_exception(exception=exception, stack=stack)
+
+    segment.add_exception(exception=Exception("newException"), stack=stack)
+    subseg.close()
+    segment.close()
+
+    seg_cause = segment.cause
+    assert isinstance(seg_cause, dict)
+    assert 'newException' == seg_cause['exceptions'][0].message
+
+
+def test_add_exception_appending_exceptions():
+    segment = Segment('seg')
+    stack = [['path', 'line', 'label']]
+    segment.add_exception(exception=Exception("testException"), stack=stack)
+    segment.add_exception(exception=Exception("newException"), stack=stack)
+    segment.close()
+
+    assert isinstance(segment.cause, dict)
+    assert len(segment.cause['exceptions']) == 2