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---
name: langchain4j-testing-strategies
description: Testing strategies for LangChain4j-powered applications. Mock LLM responses, test retrieval chains, and validate AI workflows. Use when testing AI-powered features reliably.
category: backend
tags: [langchain4j, testing, unit-tests, integration-tests, testcontainers, java, ai, llm, mock]
version: 1.1.0
allowed-tools: Read, Write, Bash
---
# LangChain4J Testing Strategies
## When to Use This Skill
Use this skill when:
- Building AI-powered applications with LangChain4J
- Writing unit tests for AI services and guardrails
- Setting up integration tests with real LLM models
- Creating mock-based tests for faster test execution
- Using Testcontainers for isolated testing environments
- Testing RAG (Retrieval-Augmented Generation) systems
- Validating tool execution and function calling
- Testing streaming responses and async operations
- Setting up end-to-end tests for AI workflows
- Implementing performance and load testing
## Instructions
To test LangChain4J applications effectively, follow these key strategies:
### 1. Start with Unit Testing
Use mock models for fast, isolated testing of business logic. See `references/unit-testing.md` for detailed examples.
```java
// Example: Mock ChatModel for unit tests
ChatModel mockModel = mock(ChatModel.class);
when(mockModel.generate(any(String.class)))
.thenReturn(Response.from(AiMessage.from("Mocked response")));
var service = AiServices.builder(AiService.class)
.chatModel(mockModel)
.build();
```
### 2. Configure Testing Dependencies
Setup proper Maven/Gradle dependencies for testing. See `references/testing-dependencies.md` for complete configuration.
**Key dependencies**:
- `langchain4j-test` - Testing utilities and guardrail assertions
- `testcontainers` - Integration testing with containerized services
- `mockito` - Mock external dependencies
- `assertj` - Better assertions
### 3. Implement Integration Tests
Test with real services using Testcontainers. See `references/integration-testing.md` for container setup examples.
```java
@Testcontainers
class OllamaIntegrationTest {
@Container
static GenericContainer<?> ollama = new GenericContainer<>(
DockerImageName.parse("ollama/ollama:latest")
).withExposedPorts(11434);
@Test
void shouldGenerateResponse() {
ChatModel model = OllamaChatModel.builder()
.baseUrl(ollama.getEndpoint())
.build();
String response = model.generate("Test query");
assertNotNull(response);
}
}
```
### 4. Test Advanced Features
For streaming responses, memory management, and complex workflows, refer to `references/advanced-testing.md`.
### 5. Apply Testing Workflows
Follow testing pyramid patterns and best practices from `references/workflow-patterns.md`.
- **70% Unit Tests**: Fast, isolated business logic testing
- **20% Integration Tests**: Real service interactions
- **10% End-to-End Tests**: Complete user workflows
## Examples
### Basic Unit Test
```java
@Test
void shouldProcessQueryWithMock() {
ChatModel mockModel = mock(ChatModel.class);
when(mockModel.generate(any(String.class)))
.thenReturn(Response.from(AiMessage.from("Test response")));
var service = AiServices.builder(AiService.class)
.chatModel(mockModel)
.build();
String result = service.chat("What is Java?");
assertEquals("Test response", result);
}
```
### Integration Test with Testcontainers
```java
@Testcontainers
class RAGIntegrationTest {
@Container
static GenericContainer<?> ollama = new GenericContainer<>(
DockerImageName.parse("ollama/ollama:latest")
);
@Test
void shouldCompleteRAGWorkflow() {
// Setup models and stores
var chatModel = OllamaChatModel.builder()
.baseUrl(ollama.getEndpoint())
.build();
var embeddingModel = OllamaEmbeddingModel.builder()
.baseUrl(ollama.getEndpoint())
.build();
var store = new InMemoryEmbeddingStore<>();
var retriever = EmbeddingStoreContentRetriever.builder()
.chatModel(chatModel)
.embeddingStore(store)
.embeddingModel(embeddingModel)
.build();
// Test complete workflow
var assistant = AiServices.builder(RagAssistant.class)
.chatLanguageModel(chatModel)
.contentRetriever(retriever)
.build();
String response = assistant.chat("What is Spring Boot?");
assertNotNull(response);
assertTrue(response.contains("Spring"));
}
}
```
## Best Practices
### Test Isolation
- Each test must be independent
- Use `@BeforeEach` and `@AfterEach` for setup/teardown
- Avoid sharing state between tests
### Mock External Dependencies
- Never call real APIs in unit tests
- Use mocks for ChatModel, EmbeddingModel, and external services
- Test error handling scenarios
### Performance Considerations
- Unit tests should run in < 50ms
- Integration tests should use container reuse
- Include timeout assertions for slow operations
### Quality Assertions
- Test both success and error scenarios
- Validate response coherence and relevance
- Include edge case testing (empty inputs, large payloads)
## Reference Documentation
For comprehensive testing guides and API references, see the included reference documents:
- **[Testing Dependencies](references/testing-dependencies.md)** - Maven/Gradle configuration and setup
- **[Unit Testing](references/unit-testing.md)** - Mock models, guardrails, and individual components
- **[Integration Testing](references/integration-testing.md)** - Testcontainers and real service testing
- **[Advanced Testing](references/advanced-testing.md)** - Streaming, memory, and error handling
- **[Workflow Patterns](references/workflow-patterns.md)** - Test pyramid and best practices
## Common Patterns
### Mock Strategy
```java
// For fast unit tests
ChatModel mockModel = mock(ChatModel.class);
when(mockModel.generate(anyString())).thenReturn(Response.from(AiMessage.from("Mocked")));
// For specific responses
when(mockModel.generate(eq("Hello"))).thenReturn(Response.from(AiMessage.from("Hi")));
when(mockModel.generate(contains("Java"))).thenReturn(Response.from(AiMessage.from("Java response")));
```
### Test Configuration
```java
// Use test-specific profiles
@TestPropertySource(properties = {
"langchain4j.ollama.base-url=http://localhost:11434"
})
class TestConfig {
// Test with isolated configuration
}
```
### Assertion Helpers
```java
// Custom assertions for AI responses
assertThat(response).isNotNull().isNotEmpty();
assertThat(response).containsAll(expectedKeywords);
assertThat(response).doesNotContain("error");
```
## Performance Requirements
- **Unit Tests**: < 50ms per test
- **Integration Tests**: Use container reuse for faster startup
- **Timeout Tests**: Include `@Timeout` for external service calls
- **Memory Management**: Test conversation window limits and cleanup
## Security Considerations
- Never use real API keys in tests
- Mock external API calls completely
- Test prompt injection detection
- Validate output sanitization
## Testing Pyramid Implementation
```
70% Unit Tests
├─ Business logic validation
├─ Guardrail testing
├─ Mock tool execution
└─ Edge case handling
20% Integration Tests
├─ Testcontainers with Ollama
├─ Vector store testing
├─ RAG workflow validation
└─ Performance benchmarking
10% End-to-End Tests
├─ Complete user journeys
├─ Real model interactions
└─ Performance under load
```
## Related Skills
- `spring-boot-test-patterns`
- `unit-test-service-layer`
- `unit-test-boundary-conditions`
## References
- [Testing Dependencies](references/testing-dependencies.md)
- [Unit Testing](references/unit-testing.md)
- [Integration Testing](references/integration-testing.md)
- [Advanced Testing](references/advanced-testing.md)
- [Workflow Patterns](references/workflow-patterns.md)