Issue #10990: Prevent tests from clobbering a set trace function.

Many tests simply didn't care if they unset a pre-existing trace function. This
made test coverage impossible. This patch fixes various tests to put back any
pre-existing trace function. It also introduces test.support.no_tracing as a
decorator which will temporarily unset the trace function for tests which
simply fail otherwise.

Thanks to Kristian Vlaardingerbroek for helping to find the cause of various
trace function unsets.

1 files changed, 6 insertions, 1 deletions

diff --git a/Lib/test/regrtest.py b/Lib/test/regrtest.py
index b5288b5..440c01d 100755
--- a/Lib/test/regrtest.py
+++ b/Lib/test/regrtest.py
@@ -827,7 +827,7 @@ class saved_test_environment:
     resources = ('sys.argv', 'cwd', 'sys.stdin', 'sys.stdout', 'sys.stderr',
                  'os.environ', 'sys.path', 'sys.path_hooks', '__import__',
                  'warnings.filters', 'asyncore.socket_map',
-                 'logging._handlers', 'logging._handlerList')
+                 'logging._handlers', 'logging._handlerList', 'sys.gettrace')
 
     def get_sys_argv(self):
         return id(sys.argv), sys.argv, sys.argv[:]
@@ -874,6 +874,11 @@ class saved_test_environment:
         sys.path_hooks = saved_hooks[1]
         sys.path_hooks[:] = saved_hooks[2]
 
+    def get_sys_gettrace(self):
+        return sys.gettrace()
+    def restore_sys_gettrace(self, trace_fxn):
+        sys.settrace(trace_fxn)
+
     def get___import__(self):
         return builtins.__import__
     def restore___import__(self, import_):