don't get the whole collection for composite index tests.

Author: ehsannas

Firestore/Example/Tests/Integration/API/FIRCompositeIndexQueryTests.mm

@@ -125,7 +125,11 @@ - (NSString *)toHashedId:(NSString *)docId {
 - (void)assertOnlineAndOfflineResultsMatch:(FIRCollectionReference *)collection
                                  withQuery:(FIRQuery *)query
                               expectedDocs:(NSArray<NSString *> *)expectedDocs {
-  [self checkOnlineAndOfflineCollection:collection
+  // `checkOnlineAndOfflineCollection` 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.
+  [self checkOnlineAndOfflineCollection:[self compositeIndexQuery:collection]
                                   query:query
                           matchesResult:[self toHashedIds:expectedDocs]];
 }

Firestore/Example/Tests/Util/FSTIntegrationTestCase.h

@@ -130,7 +130,7 @@ extern "C" {
 
 - (void)enableNetwork;
 
-- (void)checkOnlineAndOfflineCollection:(FIRCollectionReference *)collection
+- (void)checkOnlineAndOfflineCollection:(FIRQuery *)collection
                                   query:(FIRQuery *)query
                           matchesResult:(NSArray *)expectedDocs;
 

Firestore/Example/Tests/Util/FSTIntegrationTestCase.mm

@@ -636,7 +636,7 @@ - (void)enableNetwork {
  * @param query The query to check
  * @param expectedDocs Ordered list of document keys that are expected to match the query
  */
-- (void)checkOnlineAndOfflineCollection:(FIRCollectionReference *)collection
+- (void)checkOnlineAndOfflineCollection:(FIRQuery *)collection
                                   query:(FIRQuery *)query
                           matchesResult:(NSArray *)expectedDocs {
   // Note: Order matters. The following has to be done in the specific order: