run coverage should be explicit

register combine and report with atexit

buildout.cfg

@@ -24,9 +24,10 @@ eggs =
   zc.recipe.egg
   coverage
 initialization =
-  import os
-  if 'COVERAGE_PROCESS_START' not in os.environ: os.environ['COVERAGE_PROCESS_START'] = os.path.abspath('../../.coveragerc')
-  if os.getenv('COVERAGE_PROCESS_START'): import coverage; coverage.process_startup()
+  import os.path
+  from zc.buildout.testing import setup_coverage
+  path_to_coveragerc = os.path.join('${buildout:directory}', '.coveragerc')
+  setup_coverage(path_to_coveragerc)
 
 # Tests that can be run wo a network
 [oltest]

src/zc/buildout/testing.py

@@ -297,15 +297,8 @@ def buildoutSetUp(test):
     # way due to the trick above:
     os.mkdir('develop-eggs')
 
-    if os.getenv("COVERAGE_PROCESS_START"):
-        # The user has requested subprocess code coverage. Since we will be changing
-        # directories, we need to make sure this path is absolute, which means
-        # we need to temporarily return to our starting directory.
-        os.chdir(here)
-        path_to_coveragerc = os.path.abspath(os.environ['COVERAGE_PROCESS_START'])
-        os.chdir(sample)
-        assert os.path.isfile(path_to_coveragerc), path_to_coveragerc
-        os.environ['COVERAGE_PROCESS_START'] = path_to_coveragerc
+    path_to_coveragerc = os.getenv("COVERAGE_PROCESS_START", None)
+    if path_to_coveragerc is not None:
 
         # Before we return to the current directory and destroy the
         # temporary working directory, we need to copy all the coverage files
@@ -641,3 +634,41 @@ def run_buildout_in_process(command='buildout'):
         )
     command = ' '.join(command)
     run_in_process(run_buildout, command)
+
+
+def setup_coverage(path_to_coveragerc):
+    if 'RUN_COVERAGE' not in os.environ:
+        return
+    if not os.path.exists(path_to_coveragerc):
+        raise ValueError('coveragerc file %s does not exist.' % path_to_coveragerc)
+    os.environ['COVERAGE_PROCESS_START'] = path_to_coveragerc
+    rootdir = os.path.dirname(path_to_coveragerc)
+
+    def combine_report():
+        subprocess.call(
+            [
+                sys.executable, '-m', 'coverage', 'combine',
+            ],
+            cwd=rootdir,
+        )
+        subprocess.call(
+            [
+                sys.executable, '-m', 'coverage', 'report',
+            ],
+            cwd=rootdir,
+        )
+
+    if path_to_coveragerc:
+        try:
+            import coverage
+            print("Coverage configured with %s" % path_to_coveragerc)
+            if 'COVERAGE_REPORT' in os.environ:
+                import atexit
+                atexit.register(combine_report)
+            coverage.process_startup()
+        except ImportError:
+            print(
+                "You try to run coverage "
+                "but coverage is not installed in your environment."
+            )
+            sys.exit(1)