fix: truncate large test result samples to prevent oversized alert payloads (#2044)

elementary/monitor/alerts/alert_messages/builder.py

@@ -57,6 +57,7 @@
 class MessageBuilderConfig(BaseModel):
     alert_groups_subscribers: bool = False
     maximum_columns_in_alert_samples: int = 4
+    maximum_rows_in_alert_samples: int = 25
 
 
 class AlertMessageBuilder:
@@ -377,9 +378,31 @@ def _get_result_blocks(
                     and len(result_sample[0].keys())
                     <= self.config.maximum_columns_in_alert_samples
                 ):
+                    rows_to_render = result_sample
+                    omitted_rows_count = 0
+                    if len(result_sample) > self.config.maximum_rows_in_alert_samples:
+                        rows_to_render = result_sample[
+                            : self.config.maximum_rows_in_alert_samples
+                        ]
+                        omitted_rows_count = len(result_sample) - len(rows_to_render)
                     result_blocks.append(
-                        TableBlock.from_dicts(result_sample),
+                        TableBlock.from_dicts(rows_to_render),
                     )
+                    if omitted_rows_count:
+                        result_blocks.append(
+                            LinesBlock(
+                                lines=[
+                                    ItalicTextLineBlock(
+                                        text=(
+                                            f"Showing {len(rows_to_render)} of "
+                                            f"{len(result_sample)} rows "
+                                            f"({omitted_rows_count} omitted to keep "
+                                            "the alert size manageable)."
+                                        )
+                                    ),
+                                ]
+                            )
+                        )
                 else:
                     result_blocks.append(
                         JsonCodeBlock(content=result_sample),

tests/unit/alerts/alert_messages/test_result_blocks_row_truncation.py

@@ -0,0 +1,92 @@
+from typing import List
+
+from elementary.messages.blocks import ExpandableBlock, LinesBlock, TableBlock
+from elementary.monitor.alerts.alert_messages.builder import MessageBuilderConfig
+from tests.unit.alerts.alert_messages.test_alert_utils import (
+    build_base_test_alert_model,
+    get_alert_message_body,
+)
+
+
+def _build_test_rows_sample(row_count: int) -> List[dict]:
+    return [{"column1": f"value_{i}", "column2": i} for i in range(row_count)]
+
+
+def _get_test_result_expandable(message_body) -> ExpandableBlock:
+    for block in message_body.blocks:
+        if isinstance(block, ExpandableBlock) and block.title == "Test Result":
+            return block
+    raise AssertionError("Expected a 'Test Result' expandable block")
+
+
+def _get_table_block(blocks) -> TableBlock:
+    for block in blocks:
+        if isinstance(block, TableBlock):
+            return block
+    raise AssertionError("Expected a table block among the result blocks")
+
+
+def _extract_line_texts(blocks) -> List[str]:
+    texts: List[str] = []
+    for block in blocks:
+        if not isinstance(block, LinesBlock):
+            continue
+        for line in block.lines:
+            for inline in line.inlines:
+                text = getattr(inline, "text", None)
+                if text:
+                    texts.append(text)
+    return texts
+
+
+def test_large_result_sample_is_truncated_to_configured_row_limit():
+    config = MessageBuilderConfig(maximum_rows_in_alert_samples=10)
+    alert = build_base_test_alert_model(
+        status="fail",
+        table_name="test_table",
+        tags=None,
+        owners=None,
+        subscribers=None,
+        test_description=None,
+        error_message=None,
+        test_rows_sample=_build_test_rows_sample(37),
+        test_results_query=None,
+        test_params=None,
+    )
+
+    message_body = get_alert_message_body(alert, config=config)
+    result_body = _get_test_result_expandable(message_body).body
+
+    table_block = _get_table_block(result_body)
+    assert len(table_block.rows) == 10
+
+    truncation_notes = _extract_line_texts(result_body)
+    assert any(
+        "Showing 10 of 37 rows" in text and "27 omitted" in text
+        for text in truncation_notes
+    ), f"Expected a truncation note, got: {truncation_notes}"
+
+
+def test_small_result_sample_is_not_truncated():
+    config = MessageBuilderConfig(maximum_rows_in_alert_samples=10)
+    alert = build_base_test_alert_model(
+        status="fail",
+        table_name="test_table",
+        tags=None,
+        owners=None,
+        subscribers=None,
+        test_description=None,
+        error_message=None,
+        test_rows_sample=_build_test_rows_sample(3),
+        test_results_query=None,
+        test_params=None,
+    )
+
+    message_body = get_alert_message_body(alert, config=config)
+    result_body = _get_test_result_expandable(message_body).body
+
+    table_block = _get_table_block(result_body)
+    assert len(table_block.rows) == 3
+
+    truncation_notes = _extract_line_texts(result_body)
+    assert not any("omitted" in text for text in truncation_notes)