1 files changed, 75 insertions, 0 deletions
diff --git a/tests/bot/rules/test_chars.py b/tests/bot/rules/test_chars.py
new file mode 100644
index 000000000..f466a898e
--- /dev/null
+++ b/tests/bot/rules/test_chars.py
@@ -0,0 +1,75 @@
+import unittest
+
+from bot.rules import chars
+from tests.helpers import MockMessage, async_test
+
+
+def make_msg(author: str, n_chars: int) -> MockMessage:
+    """Build a message with arbitrary content of `n_chars` length."""
+    return MockMessage(author=author, content="A" * n_chars)
+
+
+class CharsRuleTests(unittest.TestCase):
+    """Tests the `chars` antispam rule."""
+
+    def setUp(self):
+        self.config = {
+            "max": 20,  # Max allowed sum of chars per user
+            "interval": 10,
+        }
+
+    @async_test
+    async def test_allows_messages_within_limit(self):
+        """Cases with a total amount of chars within limit."""
+        cases = (
+            [make_msg("bob", 0)],
+            [make_msg("bob", 20)],
+            [make_msg("bob", 15), make_msg("alice", 15)],
+        )
+
+        for recent_messages in cases:
+            last_message = recent_messages[0]
+
+            with self.subTest(last_message=last_message, recent_messages=recent_messages, config=self.config):
+                self.assertIsNone(await chars.apply(last_message, recent_messages, self.config))
+
+    @async_test
+    async def test_disallows_messages_beyond_limit(self):
+        """Cases where the total amount of chars exceeds the limit, triggering the rule."""
+        cases = (
+            (
+                [make_msg("bob", 21)],
+                "bob",
+                21,
+            ),
+            (
+                [make_msg("bob", 15), make_msg("bob", 15)],
+                "bob",
+                30,
+            ),
+            (
+                [make_msg("alice", 15), make_msg("bob", 20), make_msg("alice", 15)],
+                "alice",
+                30,
+            ),
+        )
+
+        for recent_messages, culprit, total_chars in cases:
+            last_message = recent_messages[0]
+            relevant_messages = tuple(msg for msg in recent_messages if msg.author == culprit)
+            expected_output = (
+                f"sent {total_chars} characters in {self.config['interval']}s",
+                (culprit,),
+                relevant_messages,
+            )
+
+            with self.subTest(
+                last_message=last_message,
+                recent_messages=recent_messages,
+                config=self.config,
+                expected_output=expected_output,
+            ):
+                self.assertTupleEqual(
+                    await chars.apply(last_message, recent_messages, self.config),
+                    expected_output,
+                )