Test: Turn test traceback-related variables to properties

To avoid accidental write into test-traceback-related variables, let's
turn them into properties. This makes it harder to manually fail the
test with custom exceptions, but I consider that ugly and one should
simply raise the exception and the runner should take care of setting
the class, traceback and details.

To prove the direct access is not necessary I tried this with
Avocado-vt which works without any modifications even though it uses
custom exception handling.
Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>

avocado/core/test.py

@@ -233,11 +233,11 @@ class Test(unittest.TestCase):
 
         self.log.info('START %s', self.name)
 
-        self.fail_reason = None
-        self.fail_class = None
-        self.traceback = None
         self.text_output = None
         self.__status = None
+        self.__fail_reason = None
+        self.__fail_class = None
+        self.__traceback = None
 
         self.__running = False
         self.paused = False
@@ -379,6 +379,18 @@ class Test(unittest.TestCase):
         """
         return self.__running
 
+    @property
+    def fail_reason(self):
+        return self.__fail_reason
+
+    @property
+    def fail_class(self):
+        return self.__fail_class
+
+    @property
+    def traceback(self):
+        return self.__traceback
+
     def __str__(self):
         return str(self.name)
 
@@ -654,25 +666,25 @@ class Test(unittest.TestCase):
             self._run_avocado()
         except exceptions.TestBaseException as detail:
             self.__status = detail.status
-            self.fail_class = detail.__class__.__name__
-            self.fail_reason = detail
-            self.traceback = stacktrace.prepare_exc_info(sys.exc_info())
+            self.__fail_class = detail.__class__.__name__
+            self.__fail_reason = detail
+            self.__traceback = stacktrace.prepare_exc_info(sys.exc_info())
         except AssertionError as detail:
             self.__status = 'FAIL'
-            self.fail_class = detail.__class__.__name__
-            self.fail_reason = detail
-            self.traceback = stacktrace.prepare_exc_info(sys.exc_info())
+            self.__fail_class = detail.__class__.__name__
+            self.__fail_reason = detail
+            self.__traceback = stacktrace.prepare_exc_info(sys.exc_info())
         except Exception as detail:
             self.__status = 'ERROR'
             tb_info = stacktrace.tb_info(sys.exc_info())
-            self.traceback = stacktrace.prepare_exc_info(sys.exc_info())
+            self.__traceback = stacktrace.prepare_exc_info(sys.exc_info())
             try:
-                self.fail_class = str(detail.__class__.__name__)
-                self.fail_reason = str(detail)
+                self.__fail_class = str(detail.__class__.__name__)
+                self.__fail_reason = str(detail)
             except TypeError:
-                self.fail_class = "Exception"
-                self.fail_reason = ("Unable to get exception, check the "
-                                    "traceback for details.")
+                self.__fail_class = "Exception"
+                self.__fail_reason = ("Unable to get exception, check the "
+                                      "traceback for details.")
             for e_line in tb_info:
                 self.log.error(e_line)
         finally: