Combine no longer appends by default

Combine used to always load an existing .coverage file. This lead to confusing
results and extra tox-clean steps.  Now the default is to not load the existing
file, though a new --append switch on coverage combine gets you that behavior
if you need it.

This also pointed up an issue with concurrency=multiprocessing, which is that
the child processes automatically used parallel=True, but the parent process
did not.  Now concurrency=multiprocessing implies parallel=True.

1 files changed, 3 insertions, 0 deletions

diff --git a/coverage/control.py b/coverage/control.py
index 2f2989c..f350b3d 100644
--- a/coverage/control.py
+++ b/coverage/control.py
@@ -247,6 +247,9 @@ class Coverage(object):
         if concurrency == "multiprocessing":
             patch_multiprocessing()
             concurrency = None
+            # Multi-processing uses parallel for the subprocesses, so also use
+            # it for the main process.
+            self.config.parallel = True
 
         self.collector = Collector(
             should_trace=self._should_trace,