Add CloudFormation infrastructure tests and test package setup

tests/infrastructure/test_cloudformation.py

@@ -0,0 +1,42 @@
+"""CloudFormation template validation tests.
+
+Catches issues like template size limits before deployment.
+"""
+
+from pathlib import Path
+
+import pytest
+
+CFN_DIR = Path(__file__).resolve().parents[2] / "cloudformation"
+
+# AWS CloudFormation template body size limit (bytes)
+# https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/cloudformation-limits.html
+CFN_TEMPLATE_BODY_LIMIT = 51_200
+
+
+@pytest.mark.unit
+class TestCloudFormationTemplateSizes:
+  """Ensure all CloudFormation templates stay under the inline body size limit."""
+
+  @pytest.fixture
+  def templates(self):
+    return sorted(CFN_DIR.glob("*.yaml"))
+
+  def test_templates_exist(self, templates):
+    """Sanity check that we found templates to validate."""
+    assert len(templates) > 0, f"No .yaml templates found in {CFN_DIR}"
+
+  @pytest.mark.parametrize(
+    "template",
+    sorted(CFN_DIR.glob("*.yaml")),
+    ids=lambda p: p.name,
+  )
+  def test_template_under_size_limit(self, template):
+    """Each template must be under the 51,200 byte inline body limit."""
+    size = template.stat().st_size
+    headroom = CFN_TEMPLATE_BODY_LIMIT - size
+    assert size <= CFN_TEMPLATE_BODY_LIMIT, (
+      f"{template.name} is {size:,} bytes, exceeding the "
+      f"{CFN_TEMPLATE_BODY_LIMIT:,} byte limit by {-headroom:,} bytes. "
+      f"Trim verbose outputs or switch to --template-url with S3."
+    )