test(cover): Report coverage even on tests failure

Useful to compare coverage changes when running the full test suite under Python 3 while
porting.

Makefile

@@ -17,8 +17,10 @@ PYTHON=python
 export PYTHON
 PYFLAKES=flake8
 export PYFLAKES
+VIRTUAL_ENV=./.tox/py27
 SOURCES=src/allmydata static misc setup.py
 APPNAME=tahoe-lafs
+TEST_SUITE=allmydata
 
 
 # Top-level, phony targets
@@ -31,6 +33,17 @@ default:
 ## Run all tests and code reports
 test: .tox
 	tox -p auto
+.PHONY: test-venv-coverage
+## Run all tests with coverage collection and reporting.
+test-venv-coverage:
+# Special handling for reporting coverage even when the test run fails
+	test_exit=
+	$(VIRTUAL_ENV)/bin/coverage run -m twisted.trial --rterrors --reporter=timing \
+		$(TEST_SUITE) || test_exit="$$?"
+	$(VIRTUAL_ENV)/bin/coverage combine
+	$(VIRTUAL_ENV)/bin/coverage xml || true
+	$(VIRTUAL_ENV)/bin/coverage report
+	if [ ! -z "$$test_exit" ]; then exit "$$test_exit"; fi
 
 # This is necessary only if you want to automatically produce a new
 # _version.py file from the current git history (without doing a build).

tox.ini

@@ -64,9 +64,7 @@ commands =
 
          # measuring coverage is somewhat slower than not measuring coverage
          # so only do it on request.
-         coverage: coverage run -m twisted.trial {env:TAHOE_LAFS_TRIAL_ARGS:--rterrors --reporter=timing} {posargs:{env:TEST_SUITE}}
-         coverage: coverage combine
-         coverage: coverage xml
+         coverage: make -e TEST_SUITE={posargs:{env:TEST_SUITE}} test-venv-coverage
 
 
 [testenv:integration]