Build Firestore macOS on Travis (#2645)

* Add support for testing Firestore macOS on Travis

* Firestore_{Swift,Integration}Tests_macOS don't exist yet

Author: wilhuff

.travis.yml

@@ -155,6 +155,14 @@ jobs:
       script:
         - travis_retry ./scripts/if_changed.sh ./scripts/build.sh $PROJECT $PLATFORM
 
+    - stage: test
+      env:
+        - PROJECT=Firestore PLATFORM=macOS METHOD=xcodebuild
+      before_install:
+        - ./scripts/if_changed.sh ./scripts/install_prereqs.sh
+      script:
+        - travis_retry ./scripts/if_changed.sh ./scripts/build.sh $PROJECT $PLATFORM
+
     # Firestore sanitizers
 
     - stage: test

scripts/build.sh

@@ -304,7 +304,16 @@ case "$product-$method-$platform" in
         -scheme "Firestore_IntegrationTests_$platform" \
         "${xcb_flags[@]}" \
         build
+    ;;
 
+  Firestore-xcodebuild-macOS)
+    # TODO(wilhuff): Combine with above once all targets exist
+    RunXcodebuild \
+        -workspace 'Firestore/Example/Firestore.xcworkspace' \
+        -scheme "Firestore_Tests_$platform" \
+        "${xcb_flags[@]}" \
+        build \
+        test
     ;;
 
   Firestore-cmake-macOS)