Adding first unit test for S3BucketOrigin (#31164)

There will be more unit tests to come. This first one verifies that
correct number of resources are created when re-using an OAC across two
Distributions.

packages/aws-cdk-lib/aws-cloudfront-origins/test/s3-bucket-origin.test.ts

@@ -0,0 +1,28 @@
+import { Template } from '../../assertions';
+import * as cloudfront from '../../aws-cloudfront/index';
+import * as origins from '../../aws-cloudfront-origins';
+import * as s3 from '../../aws-s3/index';
+import { Stack } from '../../core';
+
+describe('S3BucketOrigin', () => {
+  describe('withOriginAccessControl', () => {
+    test('origin can be used by multiple Distributions', () => {
+      const stack = new Stack();
+      const bucket = new s3.Bucket(stack, 'MyBucket');
+      const origin = origins.S3BucketOrigin.withOriginAccessControl(bucket);
+
+      new cloudfront.Distribution(stack, 'MyDistributionA', {
+        defaultBehavior: { origin: origin },
+      });
+      new cloudfront.Distribution(stack, 'MyDistributionB', {
+        defaultBehavior: { origin: origin },
+      });
+
+      const template = Template.fromStack(stack);
+      template.resourceCountIs('AWS::CloudFront::OriginAccessControl', 1);
+      template.resourceCountIs('AWS::CloudFront::Distribution', 2);
+      template.resourceCountIs('AWS::S3::Bucket', 1);
+      template.resourceCountIs('AWS::S3::BucketPolicy', 1);
+    });
+  });
+});