How do you test Spring AI components without calling real AI APIs?

Testing AI-integrated code without hitting real provider APIs is important for cost control, speed, and determinism. Spring AI provides two main strategies: using a MockChatModel / test double, or using the auto-configured @SpringBootTest with a property override that points to a local server or stub.

1. MockChatModel — Spring AI ships a MockChatModel that you can configure with fixed responses. Suitable for unit tests of service logic.

@Test
void shouldReturnSummary() {
    // Arrange
    ChatModel mock = new MockChatModel(
        new ChatResponse(List.of(
            new Generation(new AssistantMessage("This is a test summary.")))));

    ChatClient client = ChatClient.builder(mock).build();

    // Act
    String result = new SummaryService(client).summarise("some text");

    // Assert
    assertThat(result).isEqualTo("This is a test summary.");
}

2. WireMock / local stub server — For integration tests that need to exercise the full HTTP stack (retries, serialization, timeouts), point Spring AI at a WireMock server that returns realistic provider JSON.

# test application.properties
spring.ai.openai.base-url=http://localhost:${wiremock.server.port}
spring.ai.openai.api-key=test-key

3. Ollama with a small model — For end-to-end tests in a CI environment, run a containerised Ollama instance (via Testcontainers) with a small model like phi3:mini. Response quality is lower but the full call path is exercised.

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