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How to mock a Retrofit Response

I'm trying to mock a Retrofit Response when it isn't successful.
interface ServiceInterface {
#POST("auth/login")
suspend fun loginRequest(#Body loginInformation: LoginInformation) : Response<LoginResponse>}
I made an onSuccess test and it worked, but I don't know how to mock a Response when it isn't successful
#Test
fun onCallSuccess() = runBlocking {
val response = Response.success(LoginResponse(status = "OK", token = "TOKEN"))
coEvery {
serviceMock.loginRequest(any())
} returns response
loginRepository.doLogin("", "")
coVerify {
serviceMock.loginRequest(any())
}
assertEquals(LoginResponse(status = "OK", token = "TOKEN"), loginRepository.doLogin("",""))
}

From the retrofit documentation:
public static <T> Response<T> error(int code, okhttp3.ResponseBody body)
Create a synthetic error response with an HTTP status code of code and
body as the error body.
You should be able to make another test using Response.error similar to how you did with Response.success

Twitter oauth/request_token 200 code with empty response body

I'm implementing Twitter OAuth flows as per:
https://developer.twitter.com/en/docs/authentication/guides/log-in-with-twitter
I am getting a response back for the first step (oauth/request_token) which has a 200 code, but the response body is completely empty.
I'm using Retrofit to call the API, and have hooked up an interceptor OkHttpClient to debug the response like so:
val client = OkHttpClient.Builder().also { builder ->
builder.addInterceptor { chain ->
val request = chain.request()
val response = chain.proceed(request)
response
}
}.build()
Then setting up Retrofit like so:
Retrofit.Builder()
.baseUrl(TWITTER_AUTH_BASE_URL)
.addConverterFactory(GsonConverterFactory.create())
.client(client)
.build()
.create(TwitterAuthRetrofit::class.java)
.getRequestToken(
authorizationHeaders
).enqueue(object : Callback<TwitterRequestToken> {
override fun onResponse(call: Call<TwitterRequestToken>, response: Response<TwitterRequestToken>) {
onSuccess(response.body())
}
override fun onFailure(call: Call<TwitterRequestToken>, t: Throwable) {
onFailure()
}
})
When I debug in the interceptor, I can see the response is successful (200) but the response body is empty, which I think is causing my Gson deserialization to fail.
The result of calling response.body.contentLength() in the interceptor is -1.
The result of calling response.code in the interceptor is 200.
Here is the model I am attempting to deserialize the response body to:
data class TwitterRequestToken(
#SerializedName(value = "oauth_token")
val token: String,
#SerializedName(value = "oauth_token_secret")
val tokenSecret: String,
#SerializedName(value = "oauth_callback_confirmed")
val callbackConfirmed: Boolean
)
Note I am using #SerializedName to provide the keys for the response body, whilst the names of my properties are arbitrary to our app (we use camel case). I add a GsonConverterFactory to the Retrofit instance using the builder and have done this in the same way for many other requests before with no issues.
Here is the response I am getting from the API, which I am looking at via debugging in the interceptor above:
Response{protocol=h2, code=200, message=, url=https://api.twitter.com/oauth/request_token}
And here is the cause message from the Throwable I am getting in the onFailure callback from Retrofit:
com.google.gson.stream.MalformedJsonException:
Use JsonReader.setLenient(true) to accept malformed JSON at line 1 column 1 path $
Has anyone got any idea what might cause this?

Finally figured it out, hope this helps someone in future...
The response body from the Twitter API for oauth/request_token isn't encoded as JSON; you will need to read it from the response buffer. Specifically, when implementing the API with Retrofit, you will want your Retrofit interface to return ResponseBody (rather than your custom class), remove GSON from the Retrofit builder and, in the onResponseCallback from Retrofit, write the following code to read the buffer to a string, then split the string on & to get each key val pair, then you can split each of these on = and make sure you have all 3 values before constructing your model:
override fun onResponse(call: Call<ResponseBody>, response: Response<ResponseBody>) {
response.body()?.also { body ->
body.source().readString(Charsets.UTF_8).split('&').map { param ->
param.split('=').let { keyVal ->
keyVal[0] to keyVal[1]
}
}.toMap().let { paramMap ->
val oauthToken = paramMap["oauth_token"]
val oauthTokenSecret = paramMap["oauth_token_secret"]
val oauthCallbackConfirmed = paramMap["oauth_callback_confirmed"]?.toBoolean()
if (oauthToken == null || oauthTokenSecret == null || oauthCallbackConfirmed == null) {
onFailure()
} else {
onSuccess(
TwitterRequestToken(
oauthToken,
oauthTokenSecret,
oauthCallbackConfirmed
)
)
}
}
} ?: onFailure()
}

Retrofit doesn't send POST request

I can't seem to get the POST request working with Retrofit. My code:
ApiService.kt contains a function
#Headers("Content-Type: application/json")
#POST("resume")
suspend fun resumeAsync(#Body request: JSONObject): Response<String>
Then in my ListViewModel.kt I have a function
fun resume(id: String) {
coroutineScope.launch {
try {
val paramObject = JSONObject()
paramObject.put("id", id)
val response = Api.retrofitService.resumeAsync(paramObject)
if (response.isSuccessful) {
_status.value = "Success: Resumed!"
}
} catch (e: Exception) {
_status.value = "Failure: " + e.message
}
}
}
Why is this not working? I don't get any error or response back. If I put Log.i in the Api or the view model it says it's triggered
By debugging I found out this error:
2020-09-15 11:40:10.904 20622-20622/com.example.app I/NETWORK: Unable to create #Body converter for class org.json.JSONObject (parameter #1) for method ApiService.resumeAsync
I am using Moshi as well
private val moshi = Moshi.Builder()
.add(KotlinJsonAdapterFactory())
.build()
private val retrofit = Retrofit.Builder()
.addConverterFactory(MoshiConverterFactory.create(moshi))
.baseUrl(BASE_URL)
.build()

You can try adding a logging interceptor to your okHttp client and check what you're sending and receiving in the request.
val logging = HttpLoggingInterceptor()
logging.setLevel(HttpLoggingInterceptor.Level.BODY)
Is the url/endpoint correct?
Are you missing a "/" at the end of the url?
Have you declared internet permission in the manifest?
etc.
Solution:
Wrapping request body:
#Body body: RequestBody
val body = RequestBody.create(MediaType.parse("application/json"), obj.toString())

If you need to receive raw json then use Call<*>
#Headers("Content-Type: application/json")
#POST("resume")
fun resumeAsync(#Body request: JSONObject): retrofit2.Call<String>
Inside coroutine (without suspend keyword above)
// or .awaitResponse() to get Response<*> object
val response = Api.retrofitService.resumeAsync(paramObject).await()

Can you debug on this line
if (response.isSuccessful) {
try to check the variable response;
Or you shoud check whether the server is work, check it with other tools like Postman

So I solved my problem by doing what #Paul Nitu recommended
val body = RequestBody.create(MediaType.parse("application/json"), obj.toString())

Retry using Retrofit2 + RxJava + Jackson for 202 Status Code

I have an API which returns 200, 202, 4xx based on different scenarios. When I get a 202, I am supposed to make the same API until I get a 200 or 4xx. I tried using doOnErrorNext, onError, onNext. I was not able to crack the problem
Observable<MyPOJO> makeAPI();
Observable<MyPOJO> makeAPIImpl(){
makeAPI().doOnErrorNext(/*how to I access the error code here*/);
makeAPI().doOnNext(/*given that 202 is a success code, I expected it to come here, but it goes to Error because of JSON Mapping*/);
}
doOnErrorNext -> I was able to make the API call again but then it would happen for all the error scenarios which I dont want
I have checked multiple answers regarding this, but nobody has solved this combination specifically and am unable to incorporate other answers to my use case.

I would suggest you use OkHttp and use an interceptor to retry your request, something along these lines (this is from one of my apps in Kotlin, but it should give you the idea):
inner class ExpiredSessionInterceptor : Interceptor {
override fun intercept(chain: Interceptor.Chain): Response {
val request = chain.request()
val response = chain.proceed(request)
if (response.code() == 202) {
val newRequest = request.newBuilder().build()
return chain.proceed(newRequest)
} else {
return response;
}
}
}
then
val httpClientBuilder = OkHttpClient.Builder()
httpClientBuilder.addInterceptor(ExpiredSessionInterceptor())
val retrofit: Retrofit = Retrofit.Builder()
.baseUrl(SERVER_ENDPOINT_URL)
.addConverterFactory(GsonConverterFactory.create(gson))
.addCallAdapterFactory(RxJava2CallAdapterFactory.createWithScheduler(Schedulers.io()))
.client(httpClientBuilder.build())
.build()

Retrofit 2 - Response body null when response status is 422 (unprocessable entity)

I'm using Retrofit to make a POST Request in my web server.
However, I can't seem to get the response body when the response status is 422 (unprocessable entity). The response body is always null.
I want to know if I'm doing something wrong or if there's a workaround for this. Because I'm using the same json in the request with Postman, and it returns the body normally.
This is the method:
#Headers("Content-Type: application/vnd.api+json")
#POST("my_endpoint")
Call<JsonObject> postEntry(#Header("Authorization") String authorization, #Body JsonObject json);
The body is a JsonObject, I'm not serializing like the documentation say. But I don't think this is the problem.

By default, when your server is returning an error code response.body() is always null. What you are looking for is response.errorBody(). A common approach would be something like this:
#Override
public void onResponse(Response<JsonObject> response, Retrofit retrofit) {
if (response.isSuccess()) {
response.body(); // do something with this
} else {
response.errorBody(); // do something with that
}
}
If you need something advanced take a look at Interceptors and how to use them

I got the same error. My API was working using POSTMAN request but not working from Android retrofit call.
At first I was trying using #Field but it was getting error but later I've tried with #Body and it worked.
Sample Retrofit interface call
#POST("api/v1/app/instance")
Call<InstanceResponse> updateTokenValue(
#HeaderMap Map<String, String> headers,
#Body String body);
and API calling code is:
Map<String, String> headerMap=new HashMap<>();
headerMap.put("Accept", "application/json");
headerMap.put("Content-Type", "application/json");
headerMap.put("X-Authorization","access_token");
Map<String, String> fields = new HashMap<>();
fields.put("app_name", "video");
fields.put("app_version", "2.0.0");
fields.put("firebase_token", "token");
fields.put("primary", "1");
ApiInterface apiInterface = ApiClient.getApiClient().create(ApiInterface.class);
Call<InstanceResponse> call = apiInterface.updateTokenValue(
headerMap,new Gson().toJson(fields));

Well in this case you'll have to convert the response.
Have a look at this link
All the steps are already provided in the link above.
For Kotlin users here is the code solution.
ErrorResponse.kt (This obviously depends on your error response)
import com.squareup.moshi.Json
data class ErrorResponse(
#Json(name="name")
val name: String? = null,
#Json(name="message")
val message: String? = null,
#Json(name="errors")
val errors: Errors? = null,
#Json(name="statusCode")
val statusCode: Int? = null
)
ApiFactory.kt (Let me know if you need the entire code)
fun parseError(response: Response<*>): ErrorResponse {
val converter = ApiFactory.retrofit()
.responseBodyConverter<ErrorResponse>(
ErrorResponse::class.java, arrayOfNulls<Annotation>(0)
)
val error: ErrorResponse
try {
error = converter.convert(response.errorBody()!!)!!
} catch (e: IOException) {
e.printStackTrace()
return ErrorResponse()
}
return error
}
and in the Presenter (I use MVP)
GlobalScope.launch(Dispatchers.Main) {
try {
val response = ApiFactory.apiService.LOGIN(username, password)
.await()
val body = response.body()
body?.let {
// Handle success or any other stuff
if (it.statusCode == 200) {
mView.onSuccess(it.data!!)
}
} ?:
// This is the else part where your body is null
// Here is how you use it.
// Pass the response for error handling
mView.showMessage(ApiFactory.parseError(response).message!!)
} catch (e: Exception) {
e.printStackTrace()
}
}
And thats how you roll it!
That's All Folks!