[AI] Add tests for converter code

firebase-ai-ondevice/src/test/kotlin/com/google/firebase/ai/ondevice/ConvertersTest.kt

@@ -0,0 +1,106 @@
+/*
+ * Copyright 2026 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.firebase.ai.ondevice
+
+import com.google.common.truth.Truth.assertThat
+import com.google.firebase.ai.ondevice.interop.FinishReason as InteropFinishReason
+import com.google.firebase.ai.ondevice.interop.GenerateContentRequest as InteropGenerateContentRequest
+import com.google.firebase.ai.ondevice.interop.TextPart as InteropTextPart
+import com.google.mlkit.genai.prompt.Candidate
+import com.google.mlkit.genai.prompt.CountTokensResponse
+import org.junit.Test
+import org.mockito.Mockito.mock
+import org.mockito.Mockito.`when`
+
+internal class ConvertersTest {
+
+  // TODO: Introduce a similar tests for Images. Currently using "bitmaps" is not feasible in
+  // robolectric.
+  @Test
+  fun `InteropParts toMlKit should convert text parts correctly`() {
+    // TextPart conversion
+    val interopTextPart = InteropTextPart("hello")
+    val mlKitTextPart = interopTextPart.toMlKit()
+    assertThat(mlKitTextPart.textString).isEqualTo("hello")
+  }
+
+  @Test
+  fun `CountTokensResponse toInterop should convert correctly`() {
+    val mlKitCountTokensResponse = CountTokensResponse(42)
+    val interopCountTokensResponse = mlKitCountTokensResponse.toInterop()
+    assertThat(interopCountTokensResponse.totalTokens).isEqualTo(42)
+  }
+
+  @Test
+  fun `Candidate toInterop should convert correctly with MAX_TOKENS reason`() {
+    // There's no way of create a Candidate object, so mocking is the closest second.
+    val mlKitCandidate =
+      mock(Candidate::class.java).apply {
+        `when`(text).thenReturn("truncated text")
+        `when`(finishReason).thenReturn(Candidate.FinishReason.MAX_TOKENS)
+      }
+    val interopCandidate = mlKitCandidate.toInterop()
+    assertThat(interopCandidate.text).isEqualTo("truncated text")
+    assertThat(interopCandidate.finishReason).isEqualTo(InteropFinishReason.MAX_TOKENS)
+  }
+
+  @Test
+  fun `Candidate toInterop should map unknown finishReason to OTHER`() {
+    val mlKitCandidate =
+      mock(Candidate::class.java).apply {
+        `when`(text).thenReturn("some text")
+        `when`(finishReason).thenReturn(999) // Unknown reason
+      }
+    val interopCandidate = mlKitCandidate.toInterop()
+    assertThat(interopCandidate.finishReason).isEqualTo(InteropFinishReason.OTHER)
+  }
+
+  @Test
+  fun `GenerateContentRequest toMlKit should convert correctly and cover all fields`() {
+    val interopRequest =
+      InteropGenerateContentRequest(
+        text = InteropTextPart("prompt"),
+        temperature = 0.7f,
+        topK = 20,
+        seed = 42,
+        candidateCount = 1,
+        maxOutputTokens = 250
+      )
+    val mlKitRequest = interopRequest.toMlKit()
+
+    assertThat(mlKitRequest.text.textString).isEqualTo("prompt")
+    assertThat(mlKitRequest.temperature).isEqualTo(0.7f)
+    assertThat(mlKitRequest.topK).isEqualTo(20)
+    assertThat(mlKitRequest.seed).isEqualTo(42)
+    assertThat(mlKitRequest.candidateCount).isEqualTo(1)
+    assertThat(mlKitRequest.maxOutputTokens).isEqualTo(250)
+  }
+
+  @Test
+  fun `GenerateContentRequest toMlKit should convert correctly optional fields`() {
+    val interopRequest = InteropGenerateContentRequest(text = InteropTextPart("prompt"))
+    val mlKitRequest = interopRequest.toMlKit()
+
+    // Documented default values
+    assertThat(mlKitRequest.text.textString).isEqualTo("prompt")
+    assertThat(mlKitRequest.temperature).isEqualTo(0.0f)
+    assertThat(mlKitRequest.topK).isEqualTo(3)
+    assertThat(mlKitRequest.seed).isEqualTo(0)
+    assertThat(mlKitRequest.candidateCount).isEqualTo(1)
+    assertThat(mlKitRequest.maxOutputTokens).isEqualTo(256)
+  }
+}