Add README and helper method

Author: andrewheard

FirebaseVertexAI/Tests/Unit/Snippets/FirebaseAppSnippetsUtil.swift

@@ -17,9 +17,15 @@ import Foundation
 import XCTest
 
 extension FirebaseApp {
-  // These snippets are not invoked in CI but may be run manually by placing a
-  // GoogleService-Info.plist in the the FirebaseVertexAI/Tests/Unit/Resources folder.
-  static func configureForSnippets() throws {
+  /// Configures the default `FirebaseApp` for use in snippets tests.
+  ///
+  /// Uses a `GoogleService-Info.plist` file from the
+  /// [`Resources`](https://github.com/firebase/firebase-ios-sdk/tree/main/FirebaseVertexAI/Tests/Unit/Resources)
+  /// directory.
+  ///
+  /// > Note: This is typically called in a snippet test's set up; overriding
+  /// > `setUpWithError() throws` works well since it supports throwing errors.
+  static func configureDefaultAppForSnippets() throws {
     guard let plistPath = Bundle.module.path(
       forResource: "GoogleService-Info",
       ofType: "plist"
@@ -35,4 +41,17 @@ extension FirebaseApp {
       return
     }
   }
+
+  /// Deletes the default `FirebaseApp` if configured.
+  ///
+  /// > Note: This is typically called in a snippet test's tear down; overriding
+  /// > `tearDown() async throws` works well since deletion is asynchronous.
+  static func deleteDefaultAppForSnippets() async {
+    // Checking if `isDefaultAppConfigured()` before calling `FirebaseApp.app()` suppresses a log
+    // message that "The default Firebase app has not yet been configured." during `tearDown` when
+    // the tests are skipped. This reduces extraneous noise in the test logs.
+    if FirebaseApp.isDefaultAppConfigured(), let app = FirebaseApp.app() {
+      await app.delete()
+    }
+  }
 }

FirebaseVertexAI/Tests/Unit/Snippets/FunctionCallingSnippets.swift

@@ -16,16 +16,17 @@ import FirebaseCore
 import FirebaseVertexAI
 import XCTest
 
+// These snippet tests are intentionally skipped in CI jobs; see the README file in this directory
+// for instructions on running them manually.
+
 @available(iOS 15.0, macOS 12.0, macCatalyst 15.0, tvOS 15.0, watchOS 8.0, *)
 final class FunctionCallingSnippets: XCTestCase {
   override func setUpWithError() throws {
-    try FirebaseApp.configureForSnippets()
+    try FirebaseApp.configureDefaultAppForSnippets()
   }
 
   override func tearDown() async throws {
-    if FirebaseApp.isDefaultAppConfigured(), let app = FirebaseApp.app() {
-      await app.delete()
-    }
+    await FirebaseApp.deleteDefaultAppForSnippets()
   }
 
   func testFunctionCalling() async throws {

FirebaseVertexAI/Tests/Unit/Snippets/README.md

@@ -0,0 +1,10 @@
+# Vertex AI in Firebase Code Snippet Tests
+
+These "tests" are for verifying that the code snippets provided in our
+documentation continue to compile. They are intentionally skipped in CI but can
+be manually run to verify expected behavior / outputs.
+
+To run the tests, place a valid `GoogleService-Info.plist` file in the
+[`FirebaseVertexAI/Tests/Unit/Resources`](https://github.com/firebase/firebase-ios-sdk/tree/main/FirebaseVertexAI/Tests/Unit/Resources)
+folder. They may then be invoked individually or alongside the rest of the unit
+tests in Xcode.

FirebaseVertexAI/Tests/Unit/Snippets/StructuredOutputSnippets.swift

@@ -16,16 +16,17 @@ import FirebaseCore
 import FirebaseVertexAI
 import XCTest
 
+// These snippet tests are intentionally skipped in CI jobs; see the README file in this directory
+// for instructions on running them manually.
+
 @available(iOS 15.0, macOS 12.0, macCatalyst 15.0, tvOS 15.0, watchOS 8.0, *)
 final class StructuredOutputSnippets: XCTestCase {
   override func setUpWithError() throws {
-    try FirebaseApp.configureForSnippets()
+    try FirebaseApp.configureDefaultAppForSnippets()
   }
 
   override func tearDown() async throws {
-    if let app = FirebaseApp.app() {
-      await app.delete()
-    }
+    await FirebaseApp.deleteDefaultAppForSnippets()
   }
 
   func testStructuredOutputJSONBasic() async throws {