fix: Improve efficiency of online/offline composite index tests. (#6868)

Author: ehsannas

firebase-firestore/src/androidTest/java/com/google/firebase/firestore/testutil/CompositeIndexTestHelper.java

@@ -125,7 +125,11 @@ public void assertOnlineAndOfflineResultsMatch(
       @NonNull CollectionReference collection,
       @NonNull Query query,
       @NonNull String... expectedDocs) {
-    checkOnlineAndOfflineResultsMatch(collection, query, toHashedIds(expectedDocs));
+    // `checkOnlineAndOfflineResultsMatch` first makes sure all documents needed for
+    // `query` are in the cache. It does so making a `get` on the first argument.
+    // Since *all* composite index tests use the same collection, this is very inefficient to do.
+    // Therefore, we should only do so for tests where `TEST_ID_FIELD` matches the current test.
+    checkOnlineAndOfflineResultsMatch(this.query(collection), query, toHashedIds(expectedDocs));
   }
 
   // Asserts that the IDs in the query snapshot matches the expected Ids. The expected document

firebase-firestore/src/androidTest/java/com/google/firebase/firestore/testutil/IntegrationTestUtil.java

@@ -535,7 +535,7 @@ public static List<Object> nullList() {
    * @param expectedDocs Ordered list of document keys that are expected to match the query
    */
   public static void checkOnlineAndOfflineResultsMatch(
-      CollectionReference collection, Query query, String... expectedDocs) {
+      Query collection, Query query, String... expectedDocs) {
     // Note: Order matters. The following has to be done in the specific order:
 
     // 1- Pre-populate the cache with the entire collection.