DRY approach to typestring prefix resolution

Thanks to @kwzrd for this idea, basically we're making a constant with
the typestring prefixes and iterating that in all our converters.

These converter functions will also now raise TypeErrors if we try
to convert something that isn't in this constants list.

I've also added a new test that tests this functionality.

1 files changed, 21 insertions, 0 deletions

diff --git a/tests/bot/utils/test_redis_cache.py b/tests/bot/utils/test_redis_cache.py
index 2ce57499a..150195726 100644
--- a/tests/bot/utils/test_redis_cache.py
+++ b/tests/bot/utils/test_redis_cache.py
@@ -152,3 +152,24 @@ class RedisCacheTests(unittest.IsolatedAsyncioTestCase):
             "mega": "hungry, though",
         }
         self.assertDictEqual(await self.redis.to_dict(), result)
+
+    def test_typestring_conversion(self):
+        """Test the typestring-related helper functions."""
+        conversion_tests = (
+            (12, "i|12"),
+            (12.4, "f|12.4"),
+            ("cowabunga", "s|cowabunga"),
+        )
+
+        # Test conversion to typestring
+        for _input, expected in conversion_tests:
+            self.assertEqual(self.redis._to_typestring(_input), expected)
+
+        # Test conversion from typestrings
+        for _input, expected in conversion_tests:
+            self.assertEqual(self.redis._from_typestring(expected), _input)
+
+        # Test that exceptions are raised on invalid input
+        with self.assertRaises(TypeError):
+            self.redis._to_typestring(["internet"])
+            self.redis._from_typestring("o|firedog")