Add smoke tests for ml-modeldownloader (#2815)

Author: yifanyang

smoke-tests/build.gradle

@@ -76,6 +76,7 @@ dependencies {
   implementation "com.google.firebase:firebase-inappmessaging"
   // TODO(yifany): Restore after messaging in github is up to date
   // implementation "com.google.firebase:firebase-messaging"
+  implementation "com.google.firebase:firebase-ml-modeldownloader"
   implementation "com.google.firebase:firebase-perf"
   implementation "com.google.firebase:firebase-storage"
 

smoke-tests/src/main/java/com/google/firebase/testing/BuildOnlyTest.java

@@ -19,6 +19,7 @@
 import com.google.firebase.appindexing.FirebaseAppIndex;
 import com.google.firebase.inappmessaging.FirebaseInAppMessaging;
 // import com.google.firebase.messaging.FirebaseMessaging;
+import com.google.firebase.ml.modeldownloader.FirebaseModelDownloader;
 import com.google.firebase.perf.FirebasePerformance;
 import org.junit.Test;
 import org.junit.runner.RunWith;
@@ -45,6 +46,11 @@ public void inappmessaging_IsNotNull() {
 //    assertThat(FirebaseMessaging.getInstance()).isNotNull();
 //  }
 
+  @Test
+  public void modelDownloader_IsNotNull() {
+    assertThat(FirebaseModelDownloader.getInstance()).isNotNull();
+  }
+
   @Test
   public void performance_IsNotNull() {
     assertThat(FirebasePerformance.getInstance()).isNotNull();