Turn on ABT unit tests with SPM (#6016)

Author: paulb777

FirebaseABTesting/Tests/Unit/Utilities/ABTTestUtilities.m

@@ -20,9 +20,17 @@
 
 @implementation ABTTestUtilities
 
++ (NSBundle *)getBundle {
+#if SWIFT_PACKAGE
+  return Firebase_ABTestingUnit_SWIFTPM_MODULE_BUNDLE();
+#else
+  return [NSBundle bundleForClass:[ABTTestUtilities class]];
+#endif
+}
+
 + (ABTExperimentPayload *)payloadFromTestFilename:(NSString *)filename {
-  NSString *testJsonDataFilePath =
-      [[NSBundle bundleForClass:[ABTTestUtilities class]] pathForResource:filename ofType:@"txt"];
+  NSBundle *abtBundle = [self getBundle];
+  NSString *testJsonDataFilePath = [abtBundle pathForResource:filename ofType:@"txt"];
   NSError *readTextError = nil;
   NSString *fileText = [[NSString alloc] initWithContentsOfFile:testJsonDataFilePath
                                                        encoding:NSUTF8StringEncoding
@@ -36,8 +44,8 @@ + (ABTExperimentPayload *)payloadFromTestFilename:(NSString *)filename {
 
 + (NSData *)payloadJSONDataFromFile:(NSString *)filename
                   modifiedStartTime:(nullable NSDate *)modifiedStartTime {
-  NSString *testJsonDataFilePath =
-      [[NSBundle bundleForClass:[ABTTestUtilities class]] pathForResource:filename ofType:@"txt"];
+  NSBundle *abtBundle = [self getBundle];
+  NSString *testJsonDataFilePath = [abtBundle pathForResource:filename ofType:@"txt"];
   NSError *readTextError = nil;
   NSString *fileText = [[NSString alloc] initWithContentsOfFile:testJsonDataFilePath
                                                        encoding:NSUTF8StringEncoding

Package.swift

@@ -275,20 +275,15 @@ let package = Package(
         .define("FIRABTesting_VERSION", to: "0.0.1"), // TODO: Fix version
       ]
     ),
-    // Disabled. Pending resolution of accessing SPM resources from Objective C.
-    // See https://forums.swift.org/t/finding-swift-package-manager-resources/38058
-//    .testTarget(
-//      name: "ABTestingUnit",
-//      dependencies: ["FirebaseABTesting", "OCMock"],
-//      path: "FirebaseABTesting/Tests/Unit",
-//      resources: [.process("Resources")],
-    ////      resources: [
-    ////
-    ////        "Resources/TestABTPayload1.txt"],
-//      cSettings: [
-//        .headerSearchPath("../../.."),
-//      ]
-//    ),
+    .testTarget(
+      name: "ABTestingUnit",
+      dependencies: ["FirebaseABTesting", "OCMock"],
+      path: "FirebaseABTesting/Tests/Unit",
+      resources: [.process("Resources")],
+      cSettings: [
+        .headerSearchPath("../../.."),
+      ]
+    ),
     .target(
       name: "FirebaseAuth",
       dependencies: ["FirebaseCore",