Fix integration test failing on first Dependabot PR run

integration_tests/offline.js

@@ -0,0 +1,48 @@
+'use strict';
+
+/**
+ * Serverless plugin that intercepts CloudFormation.describeStacks during packaging.
+ *
+ * When custom Lambda layers are defined, Serverless Framework calls
+ * CloudFormation.describeStacks in compareWithLastLayer() to check whether a
+ * layer has already been uploaded (an optimisation to avoid re-uploading
+ * unchanged layers).  The error handler in that function only silences errors
+ * whose message contains "does not exist"; any other error – including the
+ * "The security token included in the request is invalid" response AWS returns
+ * when credentials are absent or invalid – is re-thrown, causing sls package
+ * to fail.
+ *
+ * In snapshot tests we never deploy, so this optimisation is meaningless.
+ * This plugin intercepts the describeStacks call and immediately returns a
+ * synthetic "does not exist" error, which the Serverless handler treats as a
+ * fresh stack and skips the comparison entirely.  The rest of the packaging
+ * lifecycle is unaffected.
+ *
+ * This shim exists because Serverless Framework has no credential-free packaging mode
+ * when custom layers are defined. Tracked upstream:
+ *   https://github.com/serverless/serverless/issues/8187 (root cause, open since 2020)
+ *   https://github.com/serverless/serverless/issues/12969 (feature request for --artifacts-only)
+ * If either issue is resolved, this plugin can be removed.
+ */
+class OfflinePackaging {
+  constructor(serverless) {
+    this.serverless = serverless;
+    this.hooks = {
+      'before:package:compileLayers': () => this.patchProvider(),
+    };
+  }
+
+  patchProvider() {
+    const provider = this.serverless.getProvider('aws');
+    const original = provider.request.bind(provider);
+    provider.request = (service, method, params, options) => {
+      if (service === 'CloudFormation' && method === 'describeStacks') {
+        const stackName = (params && params.StackName) || 'unknown';
+        return Promise.reject(new Error(`Stack with id ${stackName} does not exist`));
+      }
+      return original(service, method, params, options);
+    };
+  }
+}
+
+module.exports = OfflinePackaging;

integration_tests/serverless-extension.yml

@@ -3,6 +3,7 @@ frameworkVersion: "3"
 
 plugins:
   - ../dist/src
+  - ./offline
 
 provider:
   name: aws