@Override
    public Map<String, String> responseHeaders() {
        return unmodifiableMap(responseHeaders);
    }
@Test
    public void shouldReturnUnmodifiableResponseHeaders() throws Exception {
        DefaultGoApiResponse response = new DefaultGoApiResponse(0);
        Map<String, String> headers = response.responseHeaders();
        try {
            headers.put("new-key", "new-value");
            fail("Should not allow modification of response headers");
        } catch (UnsupportedOperationException e) {
        }
        try {
            headers.remove("key");
            fail("Should not allow modification of response headers");
        } catch (UnsupportedOperationException e) {
        }
    }