How to create webclient unit tests with Junit and Mockito?

Question

How can I create a unit test of this private method returning void using Junit4 and Mockito?

    private void fetchToken() {
        try {
        webClientBuilder.build().post().uri("http://localhost:8082/token")
                    .headers(httpHeaders -> httpHeaders.setBasicAuth("anyusername", "password")).retrieve()
                    .bodyToMono(Token.class).block();
        } catch (Exception e) {
            System.out.println("Error: " + e.getMessage());
        }

Answer 1

Using mockito like that

    @Mock
    private WebClient webClient;
    @Mock
    private WebClient.RequestBodyUriSpec uriSpec;
    @Mock
    private WebClient.RequestBodyUriSpec headerSpec;


    @Test
    void someTest(){
            WebClient.RequestBodyUriSpec bodySpec = mock(WebClient.RequestBodyUriSpec.class);
            WebClient.ResponseSpec response = mock(WebClient.ResponseSpec.class);
    
            when(webClient.post()).thenReturn(uriSpec);
            when(uriSpec.uri(uri)).thenReturn(headerSpec);
            doReturn(bodySpec).when(headerSpec).bodyValue(body);
            when(bodySpec.retrieve()).thenReturn(response);
    }