Track coverage in subprocesses

This currently only works for ./zdaemon executed from the README.rst
test.  Other tests need to be modified in a similar way (i.e. call
coverage.process_start() in the child process, if 'coverage' is
importable).

Warning: if you intend to run 'coverage report' or 'coverage xml', you
need to explicitly set COVERAGE_HOME=. or it will fail to find the
covergae information.

.coveragerc

@@ -1,6 +1,8 @@
 [run]
-source = zdaemon
+source = $COVERAGE_HOME/src/zdaemon
 omit = */tests/*, */__main__.py
+parallel = true
+data_file = $COVERAGE_HOME/.coverage
 
 [report]
 exclude_lines =

.gitignore

@@ -8,3 +8,4 @@ develop-eggs/
 eggs/
 parts/
 .coverage
+.coverage.*

src/zdaemon/tests/tests.py

@@ -378,6 +378,13 @@ def checkenv(match):
   %(ZConfig)r,
   ]
 
+try:
+    import coverage
+except ImportError:
+    pass
+else:
+    coverage.process_startup()
+
 import zdaemon.zdctl
 
 if __name__ == '__main__':

tox.ini

@@ -20,8 +20,12 @@ deps =
 usedevelop = true
 basepython =
     python2.7
+setenv =
+    COVERAGE_HOME={toxinidir}
+    COVERAGE_PROCESS_START={toxinidir}/.coveragerc
 commands =
     coverage run --source=zdaemon setup.py -q test
+    coverage combine
     coverage report
 deps =
     {[testenv]deps}