[Flow] SharedFlowException Test

coroutine/src/test/kotlin/com/murjune/practice/flow/exception/SharedFlowExceptionTest.kt

@@ -0,0 +1,131 @@
+package com.murjune.practice.flow.exception
+
+import com.murjune.practice.utils.runErrorTest
+import io.kotest.matchers.booleans.shouldBeTrue
+import io.kotest.matchers.shouldBe
+import io.kotest.matchers.types.shouldBeInstanceOf
+import kotlinx.coroutines.CoroutineExceptionHandler
+import kotlinx.coroutines.ExperimentalCoroutinesApi
+import kotlinx.coroutines.flow.MutableSharedFlow
+import kotlinx.coroutines.flow.MutableStateFlow
+import kotlinx.coroutines.flow.catch
+import kotlinx.coroutines.flow.combine
+import kotlinx.coroutines.flow.launchIn
+import kotlinx.coroutines.flow.onCompletion
+import kotlinx.coroutines.flow.onEach
+import kotlinx.coroutines.flow.onStart
+import kotlinx.coroutines.plus
+import kotlinx.coroutines.test.runCurrent
+import kotlinx.coroutines.test.runTest
+import org.junit.jupiter.api.DisplayName
+import kotlin.test.Test
+
+@OptIn(ExperimentalCoroutinesApi::class)
+class SharedFlowExceptionTest {
+    @Test
+    fun `catch 연산자를 통해 예외 처리할 수 있다`() = runTest {
+        // given
+        val sharedFlow = MutableSharedFlow<Int>()
+        val res = mutableListOf<Int>()
+        var error: Throwable? = null
+        // when
+        sharedFlow
+            .onStart { emit(1) }
+            .onEach {
+                error("error")
+            }.catch {
+                error = it
+            }.onEach {
+                res.add(it)
+            }.launchIn(backgroundScope)
+        // then
+        runCurrent()
+        res shouldBe emptyList()
+        error.shouldBeInstanceOf<IllegalStateException>()
+    }
+
+    @Test
+    @DisplayName("🚨테스트 프레임워크가 예외를 uncaught exception 으로 간주하여 테스트를 실패시킨다 따라서, runErrorTest 를 사용하여 예외를 처리한다")
+    fun `CoroutineExceptionHandler 를 통해 예외 처리할 수 있다`() = runErrorTest<IllegalStateException> {
+        // given
+        val sharedFlow = MutableSharedFlow<Int>()
+        val res = mutableListOf<Int>()
+        var error: Throwable? = null
+        val handler = CoroutineExceptionHandler { _, throwable ->
+            error = throwable
+        }
+        sharedFlow
+            .onStart { emit(1) }
+            .onEach {
+                error("error")
+            }.onEach {
+                res.add(it)
+            }.launchIn(backgroundScope + handler)
+        // then
+        runCurrent()
+        res shouldBe emptyList()
+        error.shouldBeInstanceOf<IllegalStateException>()
+    }
+
+    @Test
+    @DisplayName("🚨 catch 연산자는 예외가 발생할 때 그 예외를 처리하고, 플로우를 종료 시킨다, 그래서 다음 이벤트를 받을 수 없다")
+    fun `‼️ sharedFlow 에서 catch 연산자의 한계`() = runTest {
+        // given
+        val refreshEvent = MutableSharedFlow<Unit>()
+        val queryEvent = MutableStateFlow<String>("")
+        val res = mutableListOf<String>()
+        var isCompleted = false
+        // when
+        combine(refreshEvent.onStart { emit(Unit) }, queryEvent) { _, query ->
+            println("query: $query")
+            fetchPokemon(query)
+        }.catch {
+            println("error: $it")
+        }.onEach {
+            res.add(it)
+        }.onCompletion {
+            println(it)
+            isCompleted = true
+        }.launchIn(backgroundScope)
+        runCurrent()
+        queryEvent.value = "피카츄"
+        // then
+        runCurrent()
+        res shouldBe emptyList()
+        isCompleted.shouldBeTrue()
+    }
+
+    @Test
+    @DisplayName("📚(이 방법 추천) try catch 블록을 사용하여 예외를 처리하면, 다음 이벤트를 받을 수 있다")
+    fun `try-catch 를 활용한 예외처리`() = runTest {
+        // given
+        val refreshEvent = MutableSharedFlow<Unit>()
+        val queryEvent = MutableStateFlow<String>("")
+        val res = mutableListOf<String>()
+        // when
+        combine(refreshEvent.onStart { emit(Unit) }, queryEvent) { _, query ->
+            println("query: $query")
+            try {
+                fetchPokemon(query)
+            } catch (e: Exception) {
+                println("error: $e")
+                "error"
+            }
+        }.catch {
+            println("error: $it")
+        }.onEach {
+            if (it == "error") return@onEach
+            res.add(it)
+        }.launchIn(backgroundScope)
+        runCurrent()
+        queryEvent.value = "피카츄"
+        // then
+        runCurrent()
+        res shouldBe listOf("피카츄")
+    }
+
+    private suspend fun fetchPokemon(query: String): String {
+        if (query.isEmpty()) error("query is empty")
+        return listOf("피카츄", "라이츄", "파이리").firstOrNull { it == query }.orEmpty()
+    }
+}