Separate Snackbar Error tests from NiaAppStateTest

app/src/androidTest/kotlin/com/google/samples/apps/nowinandroid/ui/NiaAppStateTest.kt

@@ -155,7 +155,7 @@ class NiaAppStateTest {
     }
 
     @Test
-    fun niaAppState_whenErrorIsNotAdded_NullIsPresent() = runTest(UnconfinedTestDispatcher()) {
+    fun niaAppState_FirstErrorMessageIsPresent() = runTest(UnconfinedTestDispatcher()) {
         composeTestRule.setContent {
             state = NiaAppState(
                 navController = NavHostController(LocalContext.current),
@@ -164,14 +164,16 @@ class NiaAppStateTest {
                 errorMonitor = errorMonitor,
                 userNewsResourceRepository = userNewsResourceRepository,
                 timeZoneMonitor = timeZoneMonitor,
-
             )
         }
 
-        backgroundScope.launch { state.errorMessage.collect() }
+        val id = state.addErrorMessage("Test Error Message 1")
+
+        backgroundScope.launch { state.snackbarMessage.collect() }
+
         assertEquals(
-            null,
-            state.errorMessage.value,
+            id,
+            state.snackbarMessage.value?.id,
         )
     }
 }

core/data/src/test/kotlin/com/google/samples/apps/nowinandroid/core/data/util/SnackbarErrorMonitorTest.kt

@@ -0,0 +1,116 @@
+/*
+ * Copyright 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import com.google.samples.apps.nowinandroid.core.data.util.ErrorMessage
+import com.google.samples.apps.nowinandroid.core.data.util.SnackbarErrorMonitor
+import kotlinx.coroutines.flow.collect
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.test.UnconfinedTestDispatcher
+import kotlinx.coroutines.test.runTest
+import org.junit.Test
+import kotlin.test.assertEquals
+
+/**
+ * Unit tests for [SnackbarErrorMonitor].
+ */
+
+class SnackbarErrorMonitorTest {
+
+    // Subject under test.
+    private var state = SnackbarErrorMonitor()
+
+    private var message: ErrorMessage? = null
+
+    @Test
+    fun whenErrorIsNotAdded_NullIsPresent() = runTest(UnconfinedTestDispatcher()) {
+        backgroundScope.launch { state.errorMessage.collect() }
+        assertEquals(
+            null,
+            message,
+        )
+    }
+
+    @Test
+    fun whenErrorIsAdded_ErrorMessageIsPresent() = runTest(UnconfinedTestDispatcher()) {
+        backgroundScope.launch {
+            state.errorMessage.collect {
+                message = it
+            }
+        }
+
+        val id = state.addErrorMessage("Test Error Message")
+
+        assertEquals(
+            id,
+            message?.id,
+        )
+    }
+
+    @Test
+    fun whenErrorsAreAdded_FirstErrorMessageIsPresent() =
+        runTest(UnconfinedTestDispatcher()) {
+            val id1 = state.addErrorMessage("Test Error Message 1")
+            state.addErrorMessage("Test Error Message 2")
+
+            backgroundScope.launch {
+                state.errorMessage.collect {
+                    message = it
+                }
+            }
+
+            assertEquals(
+                id1,
+                message?.id,
+            )
+        }
+
+    @Test
+    fun whenErrorIsCleared_ErrorMessageIsNotPresent() =
+        runTest(UnconfinedTestDispatcher()) {
+            backgroundScope.launch {
+                state.errorMessage.collect {
+                    message = it
+                }
+            }
+            val id = state.addErrorMessage("Test Error Message 1")
+            if (id != null) {
+                state.clearErrorMessage(id)
+                assertEquals(
+                    null,
+                    message,
+                )
+            }
+        }
+
+    @Test
+    fun whenErrorsAreCleared_NextErrorMessageIsPresent() =
+        runTest(UnconfinedTestDispatcher()) {
+            backgroundScope.launch {
+                state.errorMessage.collect {
+                    message = it
+                }
+            }
+            val id1 = state.addErrorMessage("Test Error Message 1")
+            val id2 = state.addErrorMessage("Test Error Message 2")
+            if (id1 != null) {
+                state.clearErrorMessage(id1)
+                assertEquals(
+                    id2,
+                    message?.id,
+                )
+            }
+        }
+}