fix: add startup validation to ReceiptWitness config

Add Pydantic model_validator to ReceiptWitnessSettings that fails fast
if session_encryption_key is missing or a placeholder value. Conditional
validation for resend_api_key when notifications_enabled=true.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

receiptwitness/tests/conftest.py

@@ -1,12 +1,16 @@
 """Shared test fixtures."""
 
 import json
+import os
 from pathlib import Path
 
 import pytest
 
 FIXTURES_DIR = Path(__file__).parent / "fixtures"
 
+os.environ.setdefault("RW_SESSION_ENCRYPTION_KEY", "test-secret-key-for-unit-tests-only-32bytes!")
+os.environ.setdefault("RW_MAILGUN_WEBHOOK_SIGNING_KEY", "test-mailgun-signing-key")
+
 
 @pytest.fixture
 def meijer_receipt_data() -> dict:

receiptwitness/tests/test_config.py

@@ -0,0 +1,46 @@
+import pytest
+from receiptwitness.config import ReceiptWitnessSettings
+
+
+def test_valid_config():
+    s = ReceiptWitnessSettings(
+        session_encryption_key="7reF42nmTwbdN21PBoubGp7h_FU8qSimstmlaMLoRK8="
+    )
+    assert s.session_encryption_key
+
+
+def test_missing_session_encryption_key_raises():
+    with pytest.raises(ValueError, match="RW_SESSION_ENCRYPTION_KEY"):
+        ReceiptWitnessSettings(session_encryption_key="")
+
+
+def test_placeholder_session_encryption_key_raises():
+    with pytest.raises(ValueError, match="RW_SESSION_ENCRYPTION_KEY"):
+        ReceiptWitnessSettings(session_encryption_key="change-me-in-production")
+
+
+def test_notifications_enabled_without_resend_key_raises():
+    with pytest.raises(ValueError, match="RW_RESEND_API_KEY"):
+        ReceiptWitnessSettings(
+            session_encryption_key="7reF42nmTwbdN21PBoubGp7h_FU8qSimstmlaMLoRK8=",
+            notifications_enabled=True,
+            resend_api_key="",
+        )
+
+
+def test_notifications_disabled_without_resend_key_ok():
+    s = ReceiptWitnessSettings(
+        session_encryption_key="7reF42nmTwbdN21PBoubGp7h_FU8qSimstmlaMLoRK8=",
+        notifications_enabled=False,
+        resend_api_key="",
+    )
+    assert s.notifications_enabled is False
+
+
+def test_notifications_enabled_with_resend_key_ok():
+    s = ReceiptWitnessSettings(
+        session_encryption_key="7reF42nmTwbdN21PBoubGp7h_FU8qSimstmlaMLoRK8=",
+        notifications_enabled=True,
+        resend_api_key="re_test_1234567890",
+    )
+    assert s.resend_api_key == "re_test_1234567890"