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

1 files changed, 35 insertions, 0 deletions

diff --git a/Firestore/core/test/firebase/firestore/testutil/CMakeLists.txt b/Firestore/core/test/firebase/firestore/testutil/CMakeLists.txt
new file mode 100644
index 0000000..b9fcd47
--- /dev/null
+++ b/Firestore/core/test/firebase/firestore/testutil/CMakeLists.txt
@@ -0,0 +1,35 @@
+# Copyright 2018 Google
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+cc_library(
+  firebase_firestore_testutil_apple
+  SOURCES
+    app_testing.h
+    app_testing.mm
+  DEPENDS
+    FirebaseCore
+    absl_strings
+)
+
+if(APPLE)
+  list(APPEND TESTUTIL_DEPENDS firebase_firestore_testutil_apple)
+endif()
+
+add_library(
+  firebase_firestore_testutil INTERFACE
+)
+target_link_libraries(
+  firebase_firestore_testutil INTERFACE
+  ${TESTUTIL_DEPENDS}
+)