Allow throwing errors in callsFake() mock

[m-radzikowski]

Currently, the callsFake() mock does not support throwing an error from it. The error should be returned as a Client send() error, in the same way as mock.rejects() behaves.

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[bgardner-noggin]

I managed to get this to work for my code

let getParameters;
iamMock.on(GetSAMLProviderCommand.callsFake((input) => {
 getParameters = input;
 throw Error('forcing error');
});
...
expect(getParameters.Name).toEqual('Foo');

[m-radzikowski]

@bgardner-noggin this throws an error from the test that is not caught by jest, so this test fails with an error:

it('throws an error', async () => {
    snsMock.on(PublishCommand).callsFake(() => {
        throw new Error('forcing error');
    });

    const sns = new SNSClient({});

    await expect(sns.send(publishCmd1)).rejects.toThrow('forcing error');
});

However, this nudged me to look into handling errors from callsFake(), and I've just added it and released as v2.2.0.