Add ModelContent tests for fileData parts (google-gemini#163)

Author: andrewheard

Sources/GoogleAI/ModelContent.swift

@@ -35,6 +35,10 @@ public struct ModelContent: Equatable {
 
     /// URI-based data with a specified media type.
     ///
+    /// > Important: Files must be uploaded using the
+    /// > [`media.upload` REST API](https://ai.google.dev/api/rest/v1beta/media/upload) or another
+    /// > Gemini SDK.
+    ///
     /// > Note: Supported media types depends on the model; see
     /// > [supported file
     /// > formats](https://ai.google.dev/tutorials/prompting_with_media#supported_file_formats)

Tests/GoogleAITests/GoogleAITests.swift

@@ -91,6 +91,13 @@ final class GoogleGenerativeAITests: XCTestCase {
     let _ = try await genAI.generateContent(str)
     let _ = try await genAI.generateContent([str])
     let _ = try await genAI.generateContent(str, "abc", "def")
+    let _ = try await genAI.generateContent(
+      str,
+      ModelContent.Part.fileData(
+        mimetype: "image/jpeg",
+        uri: "https://generativelanguage.googleapis.com/v1beta/files/rand0mha5sh"
+      )
+    )
     #if canImport(UIKit)
       _ = try await genAI.generateContent(UIImage())
       _ = try await genAI.generateContent([UIImage()])