Issue reading `requestChecksumCalculation` when writing a test involving Upload

[sawilde]

I've been upgrading an code base to use the latest AWS-SDK packages, I have the following snippet of code that I am trying to test (that used to work on the older packages)

const uploader = new Upload({
      client: this.s3Client,
      params: {
        Bucket: destinationBucket,
        Key: destinationKey,
        Body: sourceObject.Body,
      },
      partSize: 5242880 * 4, // 20MB
    });
await uploader.done();

in the test I have configured the following mock

const mockS3 = mockClient(S3Client);

mockS3
      .on(GetObjectCommand, { Key: key, Bucket: bucket })
      .resolves({ Body: sdkStreamMixin(ReadableStream.from('x'.repeat(30e6))) });
// note: there is more mocking but I removed that for brevity as this was the minimum I needed to repeat the issue

when I run the above code it fails with this error

TypeError: Cannot read properties of undefined (reading 'requestChecksumCalculation')

I also tried defining the mock like this

const s3Client = new S3Client({ requestChecksumCalculation: 'WHEN_REQUIRED' });
const mockS3 = mockClient(s3Client);

but the same TypeError

Is there a way to define a mock of a client with specific config to get past this?