Add regression tests for limit handling in test SQL generation (#638).

Covers sqlserver__get_test_sql's `top (...)` conditional both with and
without an explicit `limit` config on a generic test. The macro currently
guards correctly (`if limit != none`); these tests trip if that guard is
ever removed or broken — without them, a regression that produced
`select top () failures …` would only surface against models where tests
actually run.

No production change.

Author: Benjamin-Knight

tests/functional/adapter/mssql/test_limit_none.py

@@ -0,0 +1,69 @@
+import pytest
+
+from dbt.tests.util import run_dbt
+
+seed_csv = """id,name
+1,alice
+2,bob
+3,charlie
+"""
+
+schema_yml = """
+version: 2
+seeds:
+  - name: test_seed
+    columns:
+      - name: id
+        tests:
+          - unique
+          - not_null
+"""
+
+schema_with_limit_yml = """
+version: 2
+seeds:
+  - name: test_seed
+    columns:
+      - name: id
+        tests:
+          - unique:
+              config:
+                limit: 10
+          - not_null:
+              config:
+                limit: 10
+"""
+
+
+class TestLimitNone:
+    @pytest.fixture(scope="class")
+    def seeds(self):
+        return {"test_seed.csv": seed_csv}
+
+    @pytest.fixture(scope="class")
+    def models(self):
+        return {"schema.yml": schema_yml}
+
+    def test_unique_test_on_seed(self, project):
+        run_dbt(["seed"])
+        results = run_dbt(["test"])
+        assert len(results) == 2
+        for result in results:
+            assert result.status == "pass"
+
+
+class TestLimitExplicit:
+    @pytest.fixture(scope="class")
+    def seeds(self):
+        return {"test_seed.csv": seed_csv}
+
+    @pytest.fixture(scope="class")
+    def models(self):
+        return {"schema.yml": schema_with_limit_yml}
+
+    def test_unique_test_with_limit(self, project):
+        run_dbt(["seed"])
+        results = run_dbt(["test"])
+        assert len(results) == 2
+        for result in results:
+            assert result.status == "pass"