add compat for pytest 3.7 and tox config for (some of) the versions i…

… could still get working

pytest_stepwise/compat.py

@@ -5,6 +5,12 @@
 except ImportError:
     from pytest_cache import Cache
 
+try:
+    # pytest 3.7+
+    Cache = Cache.for_config
+except AttributeError:
+    pass
+
 
 if hasattr(pytest, 'hookimpl'):
     tryfirst = pytest.hookimpl(tryfirst=True)

tests/test_pytest_stepwise.py

@@ -132,4 +132,7 @@ def test_stop_on_collection_errors(broken_testdir):
     result = broken_testdir.runpytest('-v', '--strict', '--stepwise', 'working_testfile.py', 'broken_testfile.py')
 
     stdout = result.stdout.str()
-    assert 'Error when collecting test' in stdout
+    if pytest.__version__ < '3.0.0':
+        assert 'Error when collecting test' in stdout
+    else:
+        assert 'errors during collection' in stdout

tox.ini

@@ -0,0 +1,15 @@
+[tox]
+envlist = py27-{pytest23,pytest27}, {py27,py36}-{pytest28,pytest29,pytest30,pytest37}
+
+[testenv]
+deps =
+    pytest23: pytest==2.3
+    pytest23: pytest-cache
+    pytest27: pytest==2.7
+    pytest27: pytest-cache
+    pytest28: pytest==2.8
+    pytest29: pytest==2.9
+    pytest30: pytest==3.0
+    pytest37: pytest==3.7
+commands =
+    py.test tests {posargs}