Add coverage generation to tox

tests/requirements.txt

@@ -5,3 +5,5 @@ virtualenv>=13.0.0
 pytest-virtualenv>=1.2.7
 pytest>=3.0.2
 wheel
+coverage
+pytest-cov

tox.ini

@@ -6,6 +6,28 @@
 
 [testenv]
 deps=-rtests/requirements.txt
+setenv=COVERAGE_FILE={toxworkdir}/.coverage.{envname}
 passenv=APPDATA USERPROFILE HOMEDRIVE HOMEPATH windir APPVEYOR
-commands=py.test {posargs}
+# These are separate so xfail tests don't count towards code coverage
+commands=pytest -m "not xfail" {posargs: "{toxinidir}" --cov-config={toxinidir}/tox.ini --cov=setuptools}
+         pytest -m "xfail"  {posargs: "{toxinidir}"}
 usedevelop=True
+
+
+[testenv:coverage]
+description=Combine coverage data and create reports
+deps=coverage
+skip_install=True
+changedir={toxworkdir}
+setenv=COVERAGE_FILE=.coverage
+commands=coverage erase
+         coverage combine
+         coverage report --rcfile={toxinidir}/tox.ini
+         coverage xml
+
+[coverage:run]
+source=setuptools
+
+[coverage:report]
+skip_covered=True
+show_missing=True