✅ add tests for message template

tests/adapters/test_template.py

@@ -0,0 +1,17 @@
+from utils import make_fake_message
+
+
+def test_message_template():
+    from nonebot.adapters import MessageTemplate
+
+    Message = make_fake_message()
+
+    template = MessageTemplate("{a:custom}{b:text}{c:image}", Message)
+
+    @template.add_format_spec
+    def custom(input: str) -> str:
+        return input + "-custom!"
+
+    formatted = template.format(a="test", b="test", c="https://example.com/test")
+    assert formatted.extract_plain_text() == "test-custom!test"
+    assert str(formatted) == "test-custom!test[fake:image]"