Make sure the pure python versions do not break.

Fixes #18

.coveragerc

@@ -1,7 +1,13 @@
 [run]
 branch = True
-source = src
+source = Persistence
 
 [report]
 precision = 2
 show_missing = True
+
+[paths]
+source =
+  src/
+  .tox/*/lib/*/site-packages/
+  .tox/pypy*/site-packages/

tox.ini

@@ -13,40 +13,43 @@ envlist =
     coverage-report,
 
 [testenv]
+install_command = pip install --no-cache-dir --no-binary=:all: {opts} {packages}
 commands =
-    {envbindir}/buildout -c {toxinidir}/buildout.cfg buildout:directory={envdir} buildout:develop={toxinidir} bootstrap
-    {envbindir}/buildout -c {toxinidir}/buildout.cfg buildout:directory={envdir} buildout:develop={toxinidir}
-    coverage run {envbindir}/test {posargs:-vc1}
-skip_install = true
+    coverage run -m zope.testrunner --test-path={envsitepackagesdir} -s Persistence {posargs:-vc1}
 deps =
-    zc.buildout
+    zope.testrunner
     coverage
 setenv =
+    PIP_NO_CACHE = 1
     COVERAGE_FILE=.coverage.{envname}
 
 [testenv:py27-pure]
 basepython =
     python2.7
 setenv =
     PURE_PYTHON = 1
+    COVERAGE_FILE=.coverage.{envname}
 
 [testenv:py35-pure]
 basepython =
     python3.5
 setenv =
     PURE_PYTHON = 1
+    COVERAGE_FILE=.coverage.{envname}
 
 [testenv:py36-pure]
 basepython =
     python3.6
 setenv =
     PURE_PYTHON = 1
+    COVERAGE_FILE=.coverage.{envname}
 
 [testenv:py37-pure]
 basepython =
     python3.7
 setenv =
     PURE_PYTHON = 1
+    COVERAGE_FILE=.coverage.{envname}
 
 [testenv:coverage-report]
 basepython = python3.6