Add a test for restoring compose content

app/src/androidTest/java/org/fnives/test/showcase/ui/AuthComposeInstrumentedTest.kt

@@ -1,5 +1,6 @@
 package org.fnives.test.showcase.ui
 
+import androidx.compose.ui.test.junit4.StateRestorationTester
 import androidx.compose.ui.test.junit4.createComposeRule
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import org.fnives.test.showcase.R
@@ -22,6 +23,7 @@ class AuthComposeInstrumentedTest : KoinTest {
 
     @get:Rule
     val composeTestRule = createComposeRule()
+    private val stateRestorationTester = StateRestorationTester(composeTestRule)
 
     private val mockServerScenarioSetupTestRule = MockServerScenarioSetupResetingTestRule()
     private val mockServerScenarioSetup get() = mockServerScenarioSetupTestRule.mockServerScenarioSetup
@@ -37,7 +39,7 @@ class AuthComposeInstrumentedTest : KoinTest {
 
     @Before
     fun setup() {
-        composeTestRule.setContent {
+        stateRestorationTester.setContent {
             AppNavigation(isUserLogeInUseCase = IsUserLoggedInUseCase(FakeUserDataLocalStorage()))
         }
         robot = ComposeLoginRobot(composeTestRule)
@@ -152,4 +154,21 @@ class AuthComposeInstrumentedTest : KoinTest {
             .assertNotLoading()
         navigationRobot.assertAuthScreen()
     }
+
+    /** GIVEN username and password WHEN restoring THEN username and password fields contain the same text */
+    @Test
+    fun restoringContentShowPreviousCredentials() {
+        composeTestRule.mainClock.advanceTimeUntil { anyResourceIdling() }
+        navigationRobot.assertAuthScreen()
+        robot.setUsername("alma")
+            .setPassword("banan")
+            .assertUsername("alma")
+            .assertPassword("banan")
+
+        stateRestorationTester.emulateSavedInstanceStateRestore()
+
+        navigationRobot.assertAuthScreen()
+        robot.assertUsername("alma")
+            .assertPassword("banan")
+    }
 }

app/src/main/java/org/fnives/test/showcase/compose/screen/auth/AuthScreenState.kt

@@ -1,7 +1,9 @@
 package org.fnives.test.showcase.compose.screen.auth
 
 import androidx.compose.runtime.*
-import androidx.compose.ui.platform.AndroidUiDispatcher
+import androidx.compose.runtime.saveable.Saver
+import androidx.compose.runtime.saveable.mapSaver
+import androidx.compose.runtime.saveable.rememberSaveable
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.launch
@@ -17,7 +19,9 @@ fun rememberAuthScreenState(
     loginUseCase: LoginUseCase = get(),
     onLoginSuccess: () -> Unit = {},
 ): AuthScreenState {
-    return remember { AuthScreenState(stateScope, loginUseCase, onLoginSuccess) }
+    return rememberSaveable(saver = AuthScreenState.getSaver(stateScope, loginUseCase, onLoginSuccess)) {
+        AuthScreenState(stateScope, loginUseCase, onLoginSuccess)
+    }
 }
 
 class AuthScreenState(
@@ -80,4 +84,23 @@ class AuthScreenState(
         UNSUPPORTED_USERNAME,
         UNSUPPORTED_PASSWORD
     }
+
+    companion object {
+        private const val USERNAME = "USERNAME"
+        private const val PASSWORD = "PASSWORD"
+
+        fun getSaver(
+            stateScope: CoroutineScope,
+            loginUseCase: LoginUseCase,
+            onLoginSuccess: () -> Unit,
+        ): Saver<AuthScreenState, *> = mapSaver(
+            save = { mapOf(USERNAME to it.username, PASSWORD to it.password) },
+            restore = {
+                AuthScreenState(stateScope, loginUseCase, onLoginSuccess).apply {
+                    onUsernameChanged(it.getOrElse(USERNAME) { "" } as String)
+                    onPasswordChanged(it.getOrElse(PASSWORD) { "" } as String)
+                }
+            }
+        )
+    }
 }

codekata/compose.instructionset.md

@@ -324,3 +324,31 @@ robot.assertErrorIsShown(R.string.something_went_wrong)
     .assertNotLoading()
 navigationRobot.assertAuthScreen()
 ```
+
+### 6. `restoringContentShowPreviousCredentials`
+
+Since we're writing apps for Android, we must handle state restoration so let's write a test for it.
+
+For simulating the recreation of the UI, we first need a `StateRestorationTester`:
+```kotlin
+    private val stateRestorationTester = StateRestorationTester(composeTestRule)
+```
+
+Then in `setup()`, we need to `setContent` on `stateRestorationTester` instead of on `composeTestRule`.
+
+Now for the actual test, we first setup the content then we trigger restoration by calling `stateRestorationTester.emulateSavedInstanceStateRestore()`, afterwards we can verify that the content is recreated in the correct way:
+
+```kotlin
+composeTestRule.mainClock.advanceTimeUntil { anyResourceIdling() }
+navigationRobot.assertAuthScreen()
+robot.setUsername("alma")
+    .setPassword("banan")
+    .assertUsername("alma")
+    .assertPassword("banan")
+
+stateRestorationTester.emulateSavedInstanceStateRestore()
+
+navigationRobot.assertAuthScreen()
+robot.assertUsername("alma")
+    .assertPassword("banan")
+```