Vfrdtyky

I have a function which makes an API call to a an external API

Let us say the function does something simple like the below. FYI need to import scala.io.Source

  def myFunction(apiRequestUrl: String) : MyObject = {

    val response: String = Source.fromURL(apiRequestUrl).mkString

    val formatedResponse: MyObject = formatResponseFunction(response)

    formatedResponse

  }

I know that some error codes I could receive are 400, 404, etc... and I'd like to just handle any error code generically from this. How could this be done? The examples I've found seem to be testing a person's own built REST API, and not function calls to someone else's external API

First of all, you have to inject the dependencies you want to replace with mocks, static calls within a function can't be mocked/stubbed

In your Scenario you have another problem that is: yor dependency Source is an object, and you can't mock objects, only non-final classes and traits. Furthermore, is considered a bad practice to mock 3rd party APIs...

A good way to solve all those problems would be to re-write the code like

trait HttpAdapter {

  def fromUrl(apiRequestUrl: String): String = Source.fromURL(apiRequestUrl).mkString

}



object HttpAdapter extends HttpAdapter



def myFunction(apiRequestUrl: String, httpAdapter: HttpAdapter = HttpAdapter) : MyObject = {

  val response: String = httpAdapter.fromUrl(apiRequestUrl)

  val formatedResponse: MyObject = formatResponseFunction(response)

  formatedResponse

}



"myFunction" should "work" in {

  //create mock

  val http = mock[HttpAdapter]



  //stub mock

  http.fromUrl("some url") shouldReturn "result"



  //inject mock

  myFunction("some url", http) shouldBe MyObject

}

Notice I've wrapped the third party API in a class I have full control over (HttpAdapter) and then I mock that one

Then I inject httpAdapter as a parameter, but I provide a default value so the callers do not need to worry about it, while I can still override it with a mock or stub in test code

Also note that I've use mockito-scala instead of regular mockito, so the stubbing syntax is different

For mocking the external service calls, you could use Mockito which is a mocking framework. Mockito is very simple to use and you can provide stubs for your external calls. For example

val m = mock[io.Source.type]

Here you mock the Source and then you provide your desired behaviour on invocation of the fromUrl function.
i.e

when(m.fromUrl("external service url")) thenReturn("result")