fix(test-execution): tolerate NULL max_query_chars in CAT batching

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: luis-dk

testgen/commands/queries/execute_tests_query.py

@@ -21,7 +21,7 @@
     is_excluded_day,
     resolve_holiday_dates,
 )
-from testgen.common.models.connection import Connection
+from testgen.common.models.connection import DEFAULT_MAX_QUERY_CHARS, Connection
 from testgen.common.models.scheduler import JobSchedule
 from testgen.common.models.table_group import TableGroup
 from testgen.common.models.test_definition import TestRunType, TestScope
@@ -534,7 +534,7 @@ def aggregate_cat_tests(
                     null_value=self.null_value,
                 )
 
-        max_query_chars = self.connection.max_query_chars - 400
+        max_query_chars = (self.connection.max_query_chars or DEFAULT_MAX_QUERY_CHARS) - 400
         groups = group_cat_tests(test_defs, max_query_chars, concat_operator, single)
 
         aggregate_queries: list[tuple[str, None]] = []

tests/unit/commands/queries/test_execute_tests_query.py

@@ -11,6 +11,8 @@
     group_cat_tests,
     parse_cat_results,
 )
+from testgen.common.database.database_service import get_flavor_service
+from testgen.common.models.connection import Connection
 
 pytestmark = pytest.mark.unit
 
@@ -478,3 +480,18 @@ def test_resolve_cat_no_freshness_result_uses_band_check(_mock_changed):
     assert operator == "NOT BETWEEN"
 
 
+def test_aggregate_cat_tests_handles_null_max_query_chars():
+    """A connection with NULL max_query_chars must not crash CAT batching — the
+    `- 400` headroom subtraction falls back to DEFAULT_MAX_QUERY_CHARS."""
+    instance = _make_execution_sql()
+    instance.connection = Connection(sql_flavor="postgresql", max_query_chars=None)
+    instance.flavor = "postgresql"
+    instance.flavor_service = get_flavor_service("postgresql")
+
+    td = _make_td(measure_expression="m_expr", condition_expression="c_expr")
+    queries, grouped_defs = instance.aggregate_cat_tests([td], single=True)
+
+    assert len(queries) == 1
+    assert grouped_defs == [[td]]
+
+