Add testGenerateContent_success_image_emptyPartIgnored

Author: andrewheard

FirebaseAI/Tests/Unit/GenerativeModelVertexAITests.swift

@@ -477,6 +477,27 @@ final class GenerativeModelVertexAITests: XCTestCase {
     XCTAssertGreaterThan(imagePart.data.count, 0)
   }
 
+  func testGenerateContent_success_image_emptyPartIgnored() async throws {
+    MockURLProtocol.requestHandler = try GenerativeModelTestUtil.httpRequestHandler(
+      forResource: "unary-success-empty-part",
+      withExtension: "json",
+      subdirectory: vertexSubdirectory
+    )
+
+    let response = try await model.generateContent(testPrompt)
+
+    XCTAssertEqual(response.candidates.count, 1)
+    let candidate = try XCTUnwrap(response.candidates.first)
+    XCTAssertEqual(candidate.content.parts.count, 2)
+    let inlineDataParts = response.inlineDataParts
+    XCTAssertEqual(inlineDataParts.count, 1)
+    let imagePart = try XCTUnwrap(inlineDataParts.first)
+    XCTAssertEqual(imagePart.mimeType, "image/png")
+    XCTAssertGreaterThan(imagePart.data.count, 0)
+    let text = try XCTUnwrap(response.text)
+    XCTAssertTrue(text.starts(with: "I can certainly help you with that"))
+  }
+
   func testGenerateContent_appCheck_validToken() async throws {
     let appCheckToken = "test-valid-token"
     model = GenerativeModel(