android - 如何对 Paging 3(PagingSource) 进行单元测试？

Question

谷歌最近宣布了新的 Paging 3 库、Kotlin-first 库、支持协程和 Flow 等。

我玩过codelab他们提供但似乎还没有任何测试支持，我还检查了documentation .他们没有提到任何关于测试的内容，所以例如我想对这个 PagingSource 进行单元测试:

 class GithubPagingSource(private val service: GithubService,
                     private val query: String) : PagingSource<Int, Repo>() {

override suspend fun load(params: LoadParams<Int>): LoadResult<Int, Repo> {
    //params.key is null in loading first page in that case we would use constant GITHUB_STARTING_PAGE_INDEX
    val position = params.key ?: GITHUB_STARTING_PAGE_INDEX
    val apiQuery = query + IN_QUALIFIER
    return try {
        val response = service.searchRepos(apiQuery, position, params.loadSize)
        val data = response.items
        LoadResult.Page(
                        data,
                        if (position == GITHUB_STARTING_PAGE_INDEX) null else position - 1,
                        if (data.isEmpty()) null else position + 1)
    }catch (IOEx: IOException){
        Log.d("GithubPagingSource", "Failed to load pages, IO Exception: ${IOEx.message}")
        LoadResult.Error(IOEx)
    }catch (httpEx: HttpException){
        Log.d("GithubPagingSource", "Failed to load pages, http Exception code: ${httpEx.code()}")
        LoadResult.Error(httpEx)
    }
  }
}  

那么，我该如何测试，有人可以帮助我吗？

Answer 1

我目前有类似的经历，发现分页库并不是真正设计为可测试的。我敢肯定，一旦它成为一个更成熟的库，Google 会使其更具可测试性。
我能够为 PagingSource 编写测试.我使用了 RxJava 3 插件和 mockito-kotlin ，但测试的总体思路应该可以在协程版本的 API 和大多数测试框架中重现。

class ItemPagingSourceTest {

    private val itemList = listOf(
            Item(id = "1"),
            Item(id = "2"),
            Item(id = "3")
    )

    private lateinit var source: ItemPagingSource

    private val service: ItemService = mock()

    @Before
    fun `set up`() {
        source = ItemPagingSource(service)
    }

    @Test
    fun `getItems - should delegate to service`() {
        val onSuccess: Consumer<LoadResult<Int, Item>> = mock()
        val onError: Consumer<Throwable> = mock()
        val params: LoadParams<Int> = mock()

        whenever(service.getItems(1)).thenReturn(Single.just(itemList))
        source.loadSingle(params).subscribe(onSuccess, onError)

        verify(service).getItems(1)
        verify(onSuccess).accept(LoadResult.Page(itemList, null, 2))
        verifyZeroInteractions(onError)
    }
}

它并不完美，因为 verify(onSuccess).accept(LoadResult.Page(itemList, null, 2))依赖 LoadResult.Page成为 data class ，可以通过其属性的值进行比较。但它确实测试了 PagingSource .