fix(integ-runner): skip region validation for snapshot tests

Author: mrgrain

packages/@aws-cdk/integ-runner/lib/engines/toolkit-lib.ts

@@ -264,7 +264,12 @@ export class ToolkitLibRunnerEngine implements ICdk {
    *
    * This catches that misconfiguration.
    */
-  private async validateRegion(asm: IReadableCloudAssembly) {
+  private async validateRegion(asm: IReadableCloudAssembly): Promise<void> {
+    // this happens for existing snapshots, in that case nothing to check
+    if (this.options.region === UNKNOWN_REGION) {
+      return;
+    }
+
     for (const stack of asm.cloudAssembly.stacksRecursively) {
       if (stack.environment.region !== this.options.region && stack.environment.region !== UNKNOWN_REGION) {
         this.ioHost.notify({

packages/@aws-cdk/integ-runner/lib/runner/snapshot-test-runner.ts

@@ -2,6 +2,7 @@ import * as path from 'path';
 import type { WritableOptions } from 'stream';
 import { Writable } from 'stream';
 import { StringDecoder } from 'string_decoder';
+import { UNKNOWN_REGION } from '@aws-cdk/cloud-assembly-api';
 import type { ResourceDifference } from '@aws-cdk/cloudformation-diff';
 import { fullDiff, formatDifferences, ResourceImpact } from '@aws-cdk/cloudformation-diff';
 import { AssemblyManifestReader } from './private/cloud-assembly';
@@ -37,7 +38,7 @@ export class IntegSnapshotRunner extends IntegRunner {
   constructor(options: Omit<IntegRunnerOptions, 'region'>) {
     super({
       ...options,
-      region: 'unused',
+      region: UNKNOWN_REGION,
     });
   }