✅ Add test to prove the fix is valid

tests/test_adapters/test_template.py

@@ -1,7 +1,15 @@
 from utils import make_fake_message
 
 
-def test_message_template():
+def test_template_basis():
+    from nonebot.adapters import MessageTemplate
+
+    template = MessageTemplate("{key:.3%}")
+    formatted = template.format(key=0.123456789)
+    assert formatted == "12.346%"
+
+
+def test_template_message():
     from nonebot.adapters import MessageTemplate
 
     Message = make_fake_message()
@@ -12,6 +20,16 @@ def test_message_template():
     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]"
+    try:
+        template.add_format_spec(custom)
+    except ValueError:
+        pass
+    else:
+        raise AssertionError("Should raise ValueError")
+
+    format_args = {"a": "custom", "b": "text", "c": "https://example.com/test"}
+    formatted = template.format(**format_args)
+
+    assert template.format_map(format_args) == formatted
+    assert formatted.extract_plain_text() == "custom-custom!text"
+    assert str(formatted) == "custom-custom!text[fake:image]"

tests/utils.py

@@ -21,9 +21,9 @@ def make_fake_message() -> Type["Message"]:
         def text(cls, text: str):
             return cls("text", {"text": text})
 
-        @classmethod
-        def image(cls, url: str):
-            return cls("image", {"url": url})
+        @staticmethod
+        def image(url: str):
+            return FakeMessageSegment("image", {"url": url})
 
         def is_text(self) -> bool:
             return self.type == "text"