Avoid importing packaging or pkg_resources for version validation (#948)

Importing the `pkg_resources` module has high memory and startup time
cost. A recent change in 102e01c already avoided it for loading extensions,
but it's still used for validating that __version__ is correctly formatted.

It is possible to avoid it by installing the `packaging` package, but
that adds a dependency for something quite trivial.

Instead, remove the validation and add tests which check the output is
as expected.

Since `setuptools` is no longer required at runtime, remove it from
`install_required`.

1 files changed, 24 insertions, 0 deletions

diff --git a/tests/test_meta.py b/tests/test_meta.py
new file mode 100644
index 0000000..10a2d33
--- /dev/null
+++ b/tests/test_meta.py
@@ -0,0 +1,24 @@
+import unittest
+from markdown.__meta__ import _get_version, __version__
+
+
+class TestVersion(unittest.TestCase):
+
+    def test_get_version(self):
+        """Test that _get_version formats __version_info__ as required by PEP 440."""
+
+        self.assertEqual(_get_version((1, 1, 2, 'dev', 0)), "1.1.2.dev0")
+        self.assertEqual(_get_version((1, 1, 2, 'alpha', 1)), "1.1.2a1")
+        self.assertEqual(_get_version((1, 2, 0, 'beta', 2)), "1.2b2")
+        self.assertEqual(_get_version((1, 2, 0, 'rc', 4)), "1.2rc4")
+        self.assertEqual(_get_version((1, 2, 0, 'final', 0)), "1.2")
+
+    def test__version__IsValid(self):
+        """Test that __version__ is valid and normalized."""
+
+        try:
+            import packaging.version
+        except ImportError:
+            from pkg_resources.extern import packaging
+
+        self.assertEqual(__version__, str(packaging.version.Version(__version__)))