Fix the text validation in header blocks

Author: seratch

slack/web/classes/blocks.py

@@ -387,7 +387,7 @@ def __init__(
 
 class HeaderBlock(Block):
     type = "header"
-    text_max_length = 3000
+    text_max_length = 150
 
     @property
     def attributes(self) -> Set[str]:
@@ -411,3 +411,7 @@ def __init__(
     @JsonValidator("text attribute must be specified")
     def _validate_text_populated(self):
         return self.text is not None
+
+    @JsonValidator(f"text attribute cannot exceed {text_max_length} characters")
+    def _validate_alt_text_length(self):
+        return self.text is None or len(self.text.text) <= self.text_max_length

tests/web/classes/test_blocks.py

@@ -713,3 +713,21 @@ def test_document(self):
         }
         self.assertDictEqual(input, HeaderBlock(**input).to_dict())
         self.assertDictEqual(input, Block.parse(input).to_dict())
+
+    def test_text_length_150(self):
+        input = {
+            "type": "header",
+            "block_id": "budget-header",
+            "text": {"type": "plain_text", "text": "1234567890" * 15},
+        }
+        HeaderBlock(**input).validate_json()
+
+    def test_text_length_151(self):
+        input = {
+            "type": "header",
+            "block_id": "budget-header",
+            "text": {"type": "plain_text", "text": ("1234567890" * 15) + "1"},
+        }
+        with self.assertRaises(SlackObjectFormationError):
+            HeaderBlock(**input).validate_json()
+