ExPlat: Handle local Experiment registration

WordPress/src/debug/java/org/wordpress/android/modules/AppComponentDebug.java

@@ -30,6 +30,7 @@
         StatsModule.class,
         TrackerModule.class,
         SuggestionSourceModule.class,
+        ExperimentModule.class,
         // Login flow library
         LoginAnalyticsModule.class,
         LoginFragmentModule.class,

WordPress/src/main/java/org/wordpress/android/modules/AppComponent.java

@@ -243,6 +243,7 @@
         ThreadModule.class,
         TrackerModule.class,
         SuggestionSourceModule.class,
+        ExperimentModule.class,
         // Login flow library
         LoginAnalyticsModule.class,
         LoginFragmentModule.class,

WordPress/src/main/java/org/wordpress/android/modules/ExperimentModule.kt

@@ -0,0 +1,13 @@
+package org.wordpress.android.modules
+
+import dagger.Module
+import dagger.multibindings.Multibinds
+import org.wordpress.android.util.experiments.Experiment
+
+@Module
+interface ExperimentModule {
+    @Multibinds fun experiments(): Set<Experiment>
+
+    // Copy and paste the line below to add a new experiment.
+    // @Binds @IntoSet fun exampleExperiment(experiment: ExampleExperiment): Experiment
+}

WordPress/src/main/java/org/wordpress/android/util/experiments/ExPlat.kt

@@ -1,9 +1,12 @@
 package org.wordpress.android.util.experiments
 
+import dagger.Lazy
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.launch
+import org.wordpress.android.BuildConfig
 import org.wordpress.android.fluxc.model.experiments.Assignments
 import org.wordpress.android.fluxc.model.experiments.Variation
+import org.wordpress.android.fluxc.model.experiments.Variation.Control
 import org.wordpress.android.fluxc.store.ExperimentStore
 import org.wordpress.android.fluxc.store.ExperimentStore.Platform
 import org.wordpress.android.fluxc.utils.AppLogWrapper
@@ -19,19 +22,21 @@ import javax.inject.Singleton
 @Singleton
 class ExPlat
 @Inject constructor(
+    private val experiments: Lazy<Set<Experiment>>,
     private val experimentStore: ExperimentStore,
     private val appLog: AppLogWrapper,
     @Named(APPLICATION_SCOPE) private val coroutineScope: CoroutineScope
 ) {
     private val platform = Platform.WORDPRESS_ANDROID
     private val activeVariations = mutableMapOf<String, Variation>()
+    private val experimentNames by lazy { experiments.get().map { it.name } }
 
     fun refreshIfNeeded() {
-        getAssignments(refreshStrategy = IF_STALE)
+        refresh(refreshStrategy = IF_STALE)
     }
 
     fun forceRefresh() {
-        getAssignments(refreshStrategy = ALWAYS)
+        refresh(refreshStrategy = ALWAYS)
     }
 
     fun clear() {
@@ -48,11 +53,27 @@ class ExPlat
      * is returned from the cached [Assignments] and then set as active. If the cached [Assignments]
      * is stale and [shouldRefreshIfStale] is `true`, then new [Assignments] are fetched and their
      * variations are going to be returned by this method on the next session.
+     *
+     * If the provided [Experiment] was not included in [ExPlat.start], then [Control] is returned.
+     * If [BuildConfig.DEBUG] is `true`, an [IllegalArgumentException] is thrown instead.
      */
-    internal fun getVariation(experiment: Experiment, shouldRefreshIfStale: Boolean) =
-            activeVariations.getOrPut(experiment.name) {
-                getAssignments(if (shouldRefreshIfStale) IF_STALE else NEVER).getVariationForExperiment(experiment.name)
-            }
+    internal fun getVariation(experiment: Experiment, shouldRefreshIfStale: Boolean): Variation {
+        if (!experimentNames.contains(experiment.name)) {
+            val message = "ExPlat: experiment not found: \"${experiment.name}\"! " +
+                    "Make sure to include it in the set provided via constructor."
+            appLog.e(T.API, message)
+            if (BuildConfig.DEBUG) throw IllegalArgumentException(message) else return Control
+        }
+        return activeVariations.getOrPut(experiment.name) {
+            getAssignments(if (shouldRefreshIfStale) IF_STALE else NEVER).getVariationForExperiment(experiment.name)
+        }
+    }
+
+    private fun refresh(refreshStrategy: RefreshStrategy) {
+        if (experimentNames.isNotEmpty()) {
+            getAssignments(refreshStrategy)
+        }
+    }
 
     private fun getAssignments(refreshStrategy: RefreshStrategy): Assignments {
         val cachedAssignments = experimentStore.getCachedAssignments() ?: Assignments()
@@ -62,7 +83,7 @@ class ExPlat
         return cachedAssignments
     }
 
-    private suspend fun fetchAssignments() = experimentStore.fetchAssignments(platform, emptyList()).also {
+    private suspend fun fetchAssignments() = experimentStore.fetchAssignments(platform, experimentNames).also {
         if (it.isError) {
             appLog.d(T.API, "ExPlat: fetching assignments failed with result: ${it.error}")
         } else {

WordPress/src/main/java/org/wordpress/android/util/experiments/ExampleExperiment.kt

@@ -0,0 +1,11 @@
+package org.wordpress.android.util.experiments
+
+import javax.inject.Inject
+
+class ExampleExperiment
+@Inject constructor(
+    exPlat: ExPlat
+) : Experiment(
+        "example_experiment",
+        exPlat
+)

WordPress/src/test/java/org/wordpress/android/util/experiments/ExPlatTest.kt

@@ -5,7 +5,9 @@ import com.nhaarman.mockitokotlin2.anyOrNull
 import com.nhaarman.mockitokotlin2.never
 import com.nhaarman.mockitokotlin2.times
 import com.nhaarman.mockitokotlin2.verify
+import com.nhaarman.mockitokotlin2.verifyZeroInteractions
 import com.nhaarman.mockitokotlin2.whenever
+import dagger.Lazy
 import org.assertj.core.api.Assertions.assertThat
 import org.junit.Before
 import org.junit.Test
@@ -26,15 +28,18 @@ import java.util.Date
 
 @RunWith(MockitoJUnitRunner::class)
 class ExPlatTest : BaseUnitTest() {
+    @Mock lateinit var experiments: Lazy<Set<Experiment>>
     @Mock lateinit var experimentStore: ExperimentStore
     @Mock lateinit var appLog: AppLogWrapper
     private lateinit var exPlat: ExPlat
     private lateinit var dummyExperiment: Experiment
 
     @Before
     fun setUp() {
-        exPlat = ExPlat(experimentStore, appLog, testScope())
+        exPlat = ExPlat(experiments, experimentStore, appLog, testScope())
         dummyExperiment = object : Experiment("dummy", exPlat) {}
+
+        setupExperiments(setOf(dummyExperiment))
     }
 
     @Test
@@ -145,6 +150,50 @@ class ExPlatTest : BaseUnitTest() {
         assertThat(secondVariation).isEqualTo(controlVariation)
     }
 
+    @Test
+    fun `forceRefresh fetches assignments if experiments is not empty`() = test {
+        setupExperiments(setOf(dummyExperiment))
+
+        exPlat.forceRefresh()
+
+        verify(experimentStore, times(1)).fetchAssignments(any(), any(), anyOrNull())
+    }
+
+    @Test
+    fun `forceRefresh does not interact with store if experiments is empty`() = test {
+        setupExperiments(emptySet())
+
+        exPlat.forceRefresh()
+
+        verifyZeroInteractions(experimentStore)
+    }
+
+    @Test
+    fun `refreshIfNeeded does not interact with store if experiments is empty`() = test {
+        setupExperiments(emptySet())
+
+        exPlat.refreshIfNeeded()
+
+        verifyZeroInteractions(experimentStore)
+    }
+
+    @Test
+    fun `getVariation does not interact with store if experiments is empty`() = test {
+        setupExperiments(emptySet())
+
+        try {
+            exPlat.getVariation(dummyExperiment, false)
+        } catch (e: IllegalArgumentException) {
+            // Do nothing.
+        } finally {
+            verifyZeroInteractions(experimentStore)
+        }
+    }
+
+    private fun setupExperiments(experiments: Set<Experiment>) {
+        whenever(this.experiments.get()).thenReturn(experiments)
+    }
+
     private suspend fun setupAssignments(cachedAssignments: Assignments?, fetchedAssignments: Assignments) {
         whenever(experimentStore.getCachedAssignments()).thenReturn(cachedAssignments)
         whenever(experimentStore.fetchAssignments(any(), any(), anyOrNull()))