Fix Firestore tests for M22 (#834)

* Add FIRFirestoreTests to the Firestore Xcode project

* Avoid waitForExpectations:timeout:

This API was added in Xcode 8.3, but we still build production releases
with Xcode 8.2. waitForExpectationsWithTimeout:handler: is available
from Xcode 7.2.

* Add AppForUnitTesting

Add a utility for constructing a Firebase App for testing.

* Handle the nil UID from FIRAuth

* Avoid running CMake tests twice

* Only build app_testing on Apple platforms

* Revise test.sh messages

2 files changed, 15 insertions, 14 deletions

diff --git a/Firestore/Example/Tests/API/FIRFirestoreTests.mm b/Firestore/Example/Tests/API/FIRFirestoreTests.mm
index 4daf35a..7cb49b7 100644
--- a/Firestore/Example/Tests/API/FIRFirestoreTests.mm
+++ b/Firestore/Example/Tests/API/FIRFirestoreTests.mm
@@ -20,21 +20,21 @@
 
 #import <XCTest/XCTest.h>
 
+#include "Firestore/core/test/firebase/firestore/testutil/app_testing.h"
+
+namespace testutil = firebase::firestore::testutil;
+
 @interface FIRFirestoreTests : XCTestCase
 @end
 
 @implementation FIRFirestoreTests
 
 - (void)testDeleteApp {
-  // Create a FIRApp for testing.
-  NSString *appName = @"custom_app_name";
-  FIROptions *options =
-      [[FIROptions alloc] initWithGoogleAppID:@"1:123:ios:123ab" GCMSenderID:@"gcm_sender_id"];
-  options.projectID = @"project_id";
-  [FIRApp configureWithName:appName options:options];
-
   // Ensure the app is set appropriately.
-  FIRApp *app = [FIRApp appNamed:appName];
+  FIRApp *app = testutil::AppForUnitTesting();
+  NSString *appName = app.name;
+  FIROptions *options = app.options;
+
   FIRFirestore *firestore = [FIRFirestore firestoreForApp:app];
   XCTAssertEqualObjects(firestore.app, app);
 
@@ -56,7 +56,10 @@
     [defaultAppDeletedExpectation fulfill];
   }];
 
-  [self waitForExpectations:@[ defaultAppDeletedExpectation ] timeout:2];
+  [self waitForExpectationsWithTimeout:2
+                               handler:^(NSError *_Nullable error) {
+                                 XCTAssertNil(error);
+                               }];
 }
 
 @end
diff --git a/Firestore/Example/Tests/SpecTests/FSTSpecTests.mm b/Firestore/Example/Tests/SpecTests/FSTSpecTests.mm
index 87e3213..43b2a5f 100644
--- a/Firestore/Example/Tests/SpecTests/FSTSpecTests.mm
+++ b/Firestore/Example/Tests/SpecTests/FSTSpecTests.mm
@@ -332,12 +332,10 @@ static NSString *const kNoIOSTag = @"no-ios";
 }
 
 - (void)doChangeUser:(id)UID {
-  if (UID == nil || [UID isEqual:[NSNull null]]) {
-    [self.driver changeUser:User::Unauthenticated()];
-  } else {
-    XCTAssert([UID isKindOfClass:[NSString class]]);
-    [self.driver changeUser:User(UID)];
+  if ([UID isEqual:[NSNull null]]) {
+    UID = nil;
   }
+  [self.driver changeUser:User::FromUid(UID)];
 }
 
 - (void)doRestart {