tox: run tests with and without cython

tox.ini

@@ -1,18 +1,39 @@
 [tox]
-envlist = py27, py36, htmlcov
+envlist = py{27,37}-{cy,nocy}, htmlcov
+package_name = cu2qu
+; we skip tox's own sdist generation as we need to pass different environment
+; variables for testing buiding with and without cython
+skipsdist = true
 
 [testenv]
+setenv =
+    nocy: CU2QU_WITH_CYTHON=0
+    cy: CU2QU_WITH_CYTHON=1
+    cy: CYTHON_TRACE=1
+    cy: CYTHON_ANNOTATE=1
 deps =
     -rtest-requirements.txt
     -rrequirements.txt
+    cy: cython
+changedir = {toxinidir}
 commands =
+    # create source distribution in a temp dir
+    python setup.py --quiet sdist --dist-dir {envtmpdir}
+
+    # install from sdist
+    python -m pip install --ignore-installed --pre --no-deps --no-cache-dir --find-links {envtmpdir} {[tox]package_name}
+
+    # ensure we are running the requested cu2qu version (compiled vs interpreted)
+    nocy: python -c "import sys, cu2qu.cu2qu; cu2qu.cu2qu.COMPILED and sys.exit(1)"
+    cy: python -c "import sys, cu2qu.cu2qu; cu2qu.cu2qu.COMPILED or sys.exit(1)"
+
+    # run tests with code coverage enabled
     coverage run --parallel-mode -m pytest {posargs}
 
 [testenv:htmlcov]
-basepython = python3.6
 deps =
     coverage
-skip_install = true
+changedir = {toxinidir}
 commands =
     coverage combine
     coverage report
@@ -23,14 +44,13 @@ passenv = *
 deps =
     coverage
     codecov
-skip_install = true
 ignore_outcome = true
+changedir = {toxinidir}
 commands =
     coverage combine
     codecov --env TRAVIS_PYTHON_VERSION
 
 [testenv:update-cython]
-skip_install = true
 deps = requests
 changedir = {toxinidir}
 commands =