Add orderByKey test

Author: schmidt-sebastian

firebase-firestore/src/test/java/com/google/firebase/firestore/local/SQLiteIndexManagerTest.java

@@ -113,6 +113,21 @@ public void testOrderByFilter() {
     verifyResults(query, "coll/val1", "coll/val3");
   }
 
+  @Test
+  public void testOrderByKeyFilter() {
+    indexManager.addFieldIndex(fieldIndex("coll", "count", Kind.ASCENDING));
+    indexManager.addFieldIndex(fieldIndex("coll", "count", Kind.DESCENDING));
+    addDoc("coll/val1", map("count", 1));
+    addDoc("coll/val2", map("count", 1));
+    addDoc("coll/val3", map("count", 3));
+
+    Query query = query("coll").orderBy(orderBy("count"));
+    verifyResults(query, "coll/val1", "coll/val2", "coll/val3");
+
+    query = query("coll").orderBy(orderBy("count", "desc"));
+    verifyResults(query, "coll/val3", "coll/val2", "coll/val1");
+  }
+
   @Test
   public void testAscendingOrderWithLessThanFilter() {
     setUpMultipleOrderBys();