Py.test 6 support (#752)

* Support Py.test 6+

* Run CI on Py.test 6 on new Pythons

Cherry-pick of commit 6e29f11

.travis.yml

@@ -14,33 +14,49 @@ matrix:
   include:
     - os: linux
       python: 2.7
+      env:
+      - PYTEST_VERSION=4.3.1
     - os: linux
       python: 2.7
       env:
       - CDECIMAL=m3-cdecimal
+      - PYTEST_VERSION=4.3.1
     - os: linux
       dist: trusty
       python: pypy
+      env:
+      - PYTEST_VERSION=4.3.1
     - os: linux
       dist: trusty
       python: pypy3
+      env:
+      - PYTEST_VERSION=6.1.2
     - os: linux
       python: 3.4
+      env:
+      - PYTEST_VERSION=4.3.1
     - os: linux
       python: 3.5
       env:
       - PYTHON_TEST_FLAGS=-bb
+      - PYTEST_VERSION=6.1.2
     - os: linux
       python: 3.6
+      env:
+      - PYTEST_VERSION=6.1.2
     - os: linux
       python: 3.7
+      env:
+      - PYTEST_VERSION=6.1.2
     - os: linux
       python: 3.8
+      env:
+      - PYTEST_VERSION=6.1.2
 
 install:
   - bash .ci/deps.${TRAVIS_OS_NAME}.sh
   - pip install --upgrade pip
-  - pip install --upgrade $CDECIMAL pytest==4.3.1 pytest-cov==2.6.1 freezegun==0.3.12
+  - pip install --upgrade $CDECIMAL pytest==$PYTEST_VERSION pytest-cov freezegun==0.3.12
   - pip install --editable .
 
 script:

conftest.py

@@ -8,4 +8,7 @@
 def pytest_collect_file(path, parent):
     if babel_path.common(path) == babel_path:
         if path.ext == ".py":
+            # TODO: remove check when dropping support for old Pytest
+            if hasattr(DoctestModule, "from_parent"):
+                return DoctestModule.from_parent(parent, fspath=path)
             return DoctestModule(path, parent)

tox.ini

@@ -3,8 +3,9 @@ envlist = py27, pypy, py34, py35, py36, py37, pypy3, py27-cdecimal
 
 [testenv]
 deps =
-    pytest==4.3.1
-    pytest-cov==2.6.1
+    pytest==4.3.1;python_version<"3.5"
+    pytest==6.1.2;python_version>="3.5"
+    pytest-cov
     cdecimal: m3-cdecimal
     freezegun==0.3.12
 whitelist_externals = make