[Vertex AI] Add integration test for generateContentStream (#14501)

Author: andrewheard

FirebaseVertexAI/Tests/TestApp/Tests/Integration/IntegrationTests.swift

@@ -90,6 +90,45 @@ final class IntegrationTests: XCTestCase {
     XCTAssertEqual(candidatesTokensDetails.tokenCount, usageMetadata.candidatesTokenCount)
   }
 
+  func testGenerateContentStream() async throws {
+    let expectedText = """
+    1.  Mercury
+    2.  Venus
+    3.  Earth
+    4.  Mars
+    5.  Jupiter
+    6.  Saturn
+    7.  Uranus
+    8.  Neptune
+    """
+    let prompt = """
+    What are the names of the planets in the solar system, ordered from closest to furthest from
+    the sun? Answer with a Markdown numbered list of the names and no other text.
+    """
+    let chat = model.startChat()
+
+    let stream = try chat.sendMessageStream(prompt)
+    var textValues = [String]()
+    for try await value in stream {
+      try textValues.append(XCTUnwrap(value.text))
+    }
+
+    let userHistory = try XCTUnwrap(chat.history.first)
+    XCTAssertEqual(userHistory.role, "user")
+    XCTAssertEqual(userHistory.parts.count, 1)
+    let promptTextPart = try XCTUnwrap(userHistory.parts.first as? TextPart)
+    XCTAssertEqual(promptTextPart.text, prompt)
+    let modelHistory = try XCTUnwrap(chat.history.last)
+    XCTAssertEqual(modelHistory.role, "model")
+    XCTAssertEqual(modelHistory.parts.count, 1)
+    let modelTextPart = try XCTUnwrap(modelHistory.parts.first as? TextPart)
+    let modelText = modelTextPart.text.trimmingCharacters(in: .whitespacesAndNewlines)
+    XCTAssertEqual(modelText, expectedText)
+    XCTAssertGreaterThan(textValues.count, 1)
+    let text = textValues.joined().trimmingCharacters(in: .whitespacesAndNewlines)
+    XCTAssertEqual(text, expectedText)
+  }
+
   func testGenerateContent_appCheckNotConfigured_shouldFail() async throws {
     let app = try FirebaseApp.defaultNamedCopy(name: TestAppCheckProviderFactory.notConfiguredName)
     addTeardownBlock { await app.delete() }