# Type of request: This is a ...
[ ] bug report
[x] feature request

# Detailed description
As a Developer,
I want to be able to simulate BadDigest and InvalidDigest errors,
So that I can test the error handling logic

## Expected behavior
https://docs.aws.amazon.com/AmazonS3/latest/API/ErrorResponses.html
BadDigest: The Content-MD5 you specified did not match what we received.
InvalidDigest: The Content-MD5 you specified is not valid.

## Actual behavior
localstack returns InvalidDigest when MD5 does not match payload.


self.client.post('{0}/functions/{1}/aliases'.format(lambda_api.PATH_ROOT, self.FUNCTION_NAME),
                         data=json.dumps({
                             'Name': self.ALIAS_NAME, 'FunctionVersion': '1', 'Description': ''}))
        response = self.client.put('{0}/functions/{1}/aliases/{2}'.format(lambda_api.PATH_ROOT, self.FUNCTION_NAME,
                                                                          self.ALIAS_NAME),
                                   data=json.dumps({'FunctionVersion': '$LATEST', 'Description': 'Test-Description'}))
        result = json.loads(response.get_data())
        result.pop('RevisionId', None)  
        expected_result = {'AliasArn': lambda_api.func_arn(self.FUNCTION_NAME) + ':' + self.ALIAS_NAME,
                           'FunctionVersion': '$LATEST', 'Description': 'Test-Description',
                           'Name': self.ALIAS_NAME}
        self.assertDictEqual(expected_result, result)
    def test_update_alias_on_non_existant_function_returns_error(self):
        with self.app.test_request_context():
            result = json.loads(lambda_api.update_alias(self.FUNCTION_NAME, self.ALIAS_NAME).get_data())
            self.assertEqual(self.RESOURCENOTFOUND_EXCEPTION, result['__type'])
            self.assertEqual(self.RESOURCENOTFOUND_MESSAGE % lambda_api.func_arn(self.FUNCTION_NAME),
                             result['message'])
    def test_update_alias_on_non_existant_alias_returns_error(self):
        with self.app.test_request_context():
            self._create_function(self.FUNCTION_NAME)
            result = json.loads(lambda_api.update_alias(self.FUNCTION_NAME, self.ALIAS_NAME).get_data())
            alias_arn = lambda_api.func_arn(self.FUNCTION_NAME) + ':' + self.ALIAS_NAME
            self.assertEqual(self.ALIASNOTFOUND_EXCEPTION, result['__type'])
            self.assertEqual(self.ALIASNOTFOUND_MESSAGE % alias_arn, result['message'])
    def test_get_alias(self):
        self._create_function(self.FUNCTION_NAME)
        self.client.post('{0}/functions/{1}/versions'.format(lambda_api.PATH_ROOT, self.FUNCTION_NAME))
        self.client.post('{0}/functions/{1}/aliases'.format(lambda_api.PATH_ROOT, self.FUNCTION_NAME),
                         data=json.dumps({