Greatly simplify tests using somewhat-hidden _pytester plugin.

Special thanks to Floris Bruynooghe for pointing me to it.

Author: ftobia

tests/conftest.py

@@ -1 +1,3 @@
 from pytest_ordering import pytest_collection_modifyitems
+
+pytest_plugins = "pytester",

tests/test_ordering.py

@@ -1,55 +1,27 @@
-import operator
-import os
-import random
 import re
 
 import pytest
 
 import pytest_ordering
+from . import numbers, words, words_backwards, grouping
 
-__here__ = os.path.dirname(os.path.abspath(__file__))
 
-
-def get_module(module_name):
-    return __import__(module_name, globals(), locals(), [], 1)
-
-
-def get_tests(module_name):
-    module = get_module(module_name)
-    return [getattr(module, t) for t in dir(module) if t.startswith('test_')]
-
-
-def _names_of_tests(output, test_file_name):
-    regex = r'^{0}:(\d+): test_([a-z]) PASSED$'.format(
-        test_file_name.replace('.', '\.'))
-    for line in output.split('\n'):
-        match = re.match(regex, line)
-        if match:
-            yield match.group(2)
-
-
-def get_order(output, test_file_name):
-    return list(_names_of_tests(output, test_file_name))
-
-
-# Default sorting is whatever order the tests show up in the module.
-
-@pytest.mark.parametrize('module_name', [
-    'numbers', 'words', 'words_backwards', 'grouping',
+@pytest.mark.parametrize('module', [
+    numbers, words, words_backwards, grouping,
 ])
-def test_ordering(module_name, capsys):
-    module = get_module(module_name)
-    pytest.main('{0}/{1}.py -vv'.format(__here__, module_name))
-    relative_filename = 'tests/{0}.py'.format(module_name)
-    out, err = capsys.readouterr()
-    assert list(module.ordering) == get_order(out, relative_filename)
+def test_ordered_tests(module, testdir):
+    items = testdir.getitems(module)
+    ordered_tests = list(pytest_ordering._order_tests(items))
+    ordered_letters = [item.name[-1] for item in ordered_tests]
+    assert ordered_letters == list(module.ordering)
 
 
 def test_run_marker_registered(capsys):
     pytest.main('--markers')
     out, err = capsys.readouterr()
     assert '@pytest.mark.run' in out
 
+
 def test_version():
     assert hasattr(pytest_ordering, '__version__')
     assert re.match(r'[0-9]+\.[0-9]+(\.[0-9]+)?$', pytest_ordering.__version__)