test(ai): add test for when the last Content has no parts

Author: thatfiredev

firebase-ai/src/main/kotlin/com/google/firebase/ai/type/Content.kt

@@ -90,13 +90,9 @@ constructor(public val role: String? = "user", public val parts: List<Part>) {
   @Serializable
   internal data class Internal(
     @EncodeDefault val role: String? = "user",
-    @EncodeDefault val parts: List<InternalPart>? = emptyList()
+    @EncodeDefault val parts: List<InternalPart> = emptyList()
   ) {
-    // TODO: add unit tests before sending a pull request (see DevAPIStreamingSnapshotTests.kt)
     internal fun toPublic(): Content {
-      if (parts.isNullOrEmpty()) {
-        return Content(role, listOf(TextPart(" ")))
-      }
       val returnedParts =
         parts.map { it.toPublic() }.filterNot { it is TextPart && it.text.isEmpty() }
       // If all returned parts were text and empty, we coalesce them into a single one-character

firebase-ai/src/test/java/com/google/firebase/ai/DevAPIStreamingSnapshotTests.kt

@@ -88,6 +88,21 @@ internal class DevAPIStreamingSnapshotTests {
       }
     }
 
+  @Test
+  fun `streaming returned the last Content without parts`() =
+    goldenDevAPIStreamingFile("streaming-success-no-content-parts.txt") {
+      val responses = model.generateContentStream("prompt")
+
+      withTimeout(testTimeout) {
+        val responseList = responses.toList()
+        responseList.isEmpty() shouldBe false
+        responseList.last().candidates.first().apply {
+          finishReason shouldBe FinishReason.STOP
+          content.parts.isEmpty() shouldBe false
+        }
+      }
+    }
+
   @Test
   fun `stopped for recitation`() =
     goldenDevAPIStreamingFile("streaming-failure-recitation-no-content.txt") {