Fix #5895: Support feature flag toggling in StateFragmentTest

app/src/sharedTest/java/org/oppia/android/app/player/state/StateFragmentTest.kt

@@ -5830,14 +5830,61 @@ class StateFragmentTest {
     }
   }
 
+  @Test
+  fun testFlashback_featureFlagOff_thenFeatureFlagOn() {
+    // Set up the previous app instance with the flashback feature flag OFF.
+    TestPlatformParameterModule.forceEnableFlashbackSupport(false)
+    executeInPreviousAppInstance { _ -> }
+
+    // In the current app instance, enable the feature flag and verify flashback button is shown.
+    setUpTestWithFlashbackFeatureOn()
+    launchForExploration(TEST_EXPLORATION_ID_2, shouldSavePartialProgress = false).use {
+      startPlayingExploration()
+
+      navigateToPrototypeRatioInputState()
+
+      // Submit wrong answer.
+      typeRatioExpression("4:8")
+      clickSubmitAnswerButton()
+
+      // Verify flashback button is visible.
+      scrollToViewType(FLASHBACK_BUTTON)
+      onView(withId(R.id.flashback_button)).check(
+        matches(withText(R.string.state_flashback_button))
+      )
+    }
+  }
+
+  @Test
+  fun testFlashback_featureFlagOn_persistsAcrossAppInstances() {
+    // Set up the previous app instance with the flashback feature flag ON.
+    TestPlatformParameterModule.forceEnableFlashbackSupport(true)
+    executeInPreviousAppInstance { _ -> }
+
+    // In the current app instance, flag should still be on.
+    setUpTestWithFlashbackFeatureOn()
+    launchForExploration(TEST_EXPLORATION_ID_2, shouldSavePartialProgress = false).use {
+      startPlayingExploration()
+
+      navigateToPrototypeRatioInputState()
+
+      // Submit wrong answer.
+      typeRatioExpression("4:8")
+      clickSubmitAnswerButton()
+
+      // Verify flashback button IS shown (flag persisted across app instances).
+      scrollToViewType(FLASHBACK_BUTTON)
+      onView(withId(R.id.flashback_button)).check(matches(isDisplayed()))
+    }
+  }
+
   @Test
   fun testStateFragment_submitMultipleChoiceAnswer_verifyMultipleChoiceSubmittedAnswer() {
     setUpTestWithFlashbackFeatureOn()
     launchForExploration(TEST_EXPLORATION_ID_2, shouldSavePartialProgress = false).use {
       startPlayingExploration()
       playThroughPrototypeState1()
       playThroughPrototypeState2()
-
       // Submit Multiple choice answer.
       selectMultipleChoiceOption(optionPosition = 2, expectedOptionText = "Eagle")
       clickSubmitAnswerButton()
@@ -7075,6 +7122,31 @@ class StateFragmentTest {
     fun isOnRobolectric(): Boolean
   }
 
+  /**
+   * Creates a separate test application component and executes the specified block. This should be
+   * called before setUpTestApplicationComponent to avoid undefined behavior in production code.
+   * This can be used to simulate arranging state in a "prior" run of the app.
+   *
+   * Note that only dependencies fetched from the specified [TestApplicationComponent] should be
+   * used, not any class-level injected dependencies.
+   */
+  private fun executeInPreviousAppInstance(block: (TestApplicationComponent) -> Unit) {
+    val testApplication = TestApplication()
+    // The true application is hooked as a base context. This is to make sure the new application
+    // can behave like a real Android application class (per Robolectric) without having a shared
+    // Dagger dependency graph with the application under test.
+    testApplication.attachBaseContext(ApplicationProvider.getApplicationContext())
+    block(
+      DaggerStateFragmentTest_TestApplicationComponent.builder()
+        .setApplication(testApplication)
+        .build()
+    )
+
+    // Resetting after the previous instance is important so that the next (main) app instance
+    // can set its own flags.
+    TestPlatformParameterModule.reset()
+  }
+
   class TestApplication : Application(), ActivityComponentFactory, ApplicationInjectorProvider {
     private val component: TestApplicationComponent by lazy {
       DaggerStateFragmentTest_TestApplicationComponent.builder()
@@ -7090,6 +7162,10 @@ class StateFragmentTest {
       return component.getActivityComponentBuilderProvider().get().setActivity(activity).build()
     }
 
+    public override fun attachBaseContext(base: Context?) {
+      super.attachBaseContext(base)
+    }
+
     override fun getApplicationInjector(): ApplicationInjector = component
   }