when(mockClient.filterWithHeader(headers)).thenReturn(mockNewClient);

        final Client result = fesenClient.filterWithHeader(headers);

        assertTrue(fesenClient == result); // Should return this
        assertTrue(mockNewClient == fesenClient.client); // Internal client should be updated
        verify(mockClient).filterWithHeader(headers);
    }

    /**

            final Request request, final ActionListener<Response> listener) {
        client.execute(action, request, listener);
    }

    @Override
    public Client filterWithHeader(final Map<String, String> headers) {
        client = client.filterWithHeader(headers);
        return this;
    }

    /**
     * Deletes documents matching the specified query using scroll and bulk delete.
     *

     *
     * @param headers the headers to add to requests
     * @return the filtered client
     */
    @Override
    public Client filterWithHeader(final Map<String, String> headers) {
        return client.filterWithHeader(headers);
    }

    /**
     * Executes an action asynchronously.
     *
     * @param <Request>  the request type