Revert "Stop requiring pytest-subtests, it has been incorporated into pytest."

This reverts commit e97a3c1.

Author: StanFromIreland

tests/test_contents.py

@@ -8,6 +8,24 @@
     import importlib_resources as resources
 
 
+if sys.version_info < (3, 6):
+    # pytest-subtests does not support Python < 3.6, but having the tests
+    # separated into clean subtests is nice but not required, so we will create
+    # a stub that does nothing but at least doesn't fail for lack of a fixture.
+    import contextlib
+
+    class _SubTestStub:
+        @contextlib.contextmanager
+        def test(self, **kwargs):
+            yield
+
+    _sub_test_stub = _SubTestStub()
+
+    @pytest.fixture
+    def subtests():
+        yield _sub_test_stub
+
+
 def get_magic(zone_name):
     components = zone_name.split("/")
     package_name = ".".join(["tzdata.zoneinfo"] + components[:-1])

tox.ini

@@ -7,6 +7,7 @@ skip_missing_interpreters = true
 description = Test that the tzdata contents are accessible
 deps =
     pytest
+    pytest-subtests; python_version>='3.6'
     importlib_resources; python_version<'3.7'
 commands =
     pytest {toxinidir} {posargs}