test(backend): add failing tests for step 6 — AiService

backend/src/test/kotlin/com/condado/newsletter/service/AiServiceTest.kt

@@ -0,0 +1,88 @@
+package com.condado.newsletter.service
+
+import com.condado.newsletter.model.ParsedAiResponse
+import io.mockk.every
+import io.mockk.mockk
+import io.mockk.verify
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.assertThrows
+import org.springframework.web.client.RestClient
+
+class AiServiceTest {
+
+    private val mockRestClient: RestClient = mockk()
+    private val mockRequestBodyUriSpec: RestClient.RequestBodyUriSpec = mockk()
+    private val mockRequestBodySpec: RestClient.RequestBodySpec = mockk()
+    private val mockResponseSpec: RestClient.ResponseSpec = mockk()
+
+    private val service = AiService(
+        restClient = mockRestClient,
+        apiKey = "test-key",
+        model = "gpt-4o"
+    )
+
+    @Test
+    fun should_returnAiResponseText_when_apiCallSucceeds() {
+        val rawResponse = "SUBJECT: Test Subject\nBODY:\nTest body content"
+        stubRestClient(rawResponse)
+
+        val result = service.generate("My test prompt")
+
+        assertThat(result.subject).isEqualTo("Test Subject")
+        assertThat(result.body).isEqualTo("Test body content")
+    }
+
+    @Test
+    fun should_throwAiServiceException_when_apiReturnsError() {
+        every { mockRestClient.post() } throws RuntimeException("API unavailable")
+
+        assertThrows<AiServiceException> {
+            service.generate("My prompt")
+        }
+    }
+
+    @Test
+    fun should_extractSubjectAndBody_when_responseIsWellFormatted() {
+        val raw = "SUBJECT: Weekly Update\nBODY:\nDear colleagues,\n\nPlease note the snacks."
+        val result = service.parseResponse(raw)
+
+        assertThat(result.subject).isEqualTo("Weekly Update")
+        assertThat(result.body).isEqualTo("Dear colleagues,\n\nPlease note the snacks.")
+    }
+
+    @Test
+    fun should_throwParseException_when_responseIsMissingSubjectLine() {
+        val raw = "BODY:\nSome body without a subject"
+
+        assertThrows<AiParseException> {
+            service.parseResponse(raw)
+        }
+    }
+
+    @Test
+    fun should_throwParseException_when_responseIsMissingBodySection() {
+        val raw = "SUBJECT: Some Subject\nNo body section here"
+
+        assertThrows<AiParseException> {
+            service.parseResponse(raw)
+        }
+    }
+
+    // ── helper ──────────────────────────────────────────────────────────────
+
+    private fun stubRestClient(responseText: String) {
+        every { mockRestClient.post() } returns mockRequestBodyUriSpec
+        every { mockRequestBodyUriSpec.uri(any<String>()) } returns mockRequestBodySpec
+        every { mockRequestBodySpec.header(any(), any()) } returns mockRequestBodySpec
+        every { mockRequestBodySpec.body(any<Any>()) } returns mockRequestBodySpec
+        every { mockRequestBodySpec.retrieve() } returns mockResponseSpec
+        every { mockResponseSpec.body(String::class.java) } returns """
+            {
+              "choices": [
+                { "message": { "content": "$responseText" } }
+              ]
+            }
+        """.trimIndent()
+    }
+}