Test Utilities

A few test utility classes that are generally useful when testing your application are packaged as part of spring-boot.

ConfigDataApplicationContextInitializer

ConfigDataApplicationContextInitializer is an ApplicationContextInitializer that you can apply to your tests to load Spring Boot application.properties files. You can use it when you do not need the full set of features provided by @SpringBootTest, as shown in the following example:

import org.springframework.boot.test.context.ConfigDataApplicationContextInitializer;
import org.springframework.test.context.ContextConfiguration;

@ContextConfiguration(classes = Config.class, initializers = ConfigDataApplicationContextInitializer.class)
class MyConfigFileTests {

	// ...

}

Using ConfigDataApplicationContextInitializer alone does not provide support for @Value("${…}") injection. Its only job is to ensure that application.properties files are loaded into Spring’s Environment. For @Value support, you need to either additionally configure a PropertySourcesPlaceholderConfigurer or use @SpringBootTest, which auto-configures one for you.

TestPropertyValues

TestPropertyValues lets you quickly add properties to a ConfigurableEnvironment or ConfigurableApplicationContext. You can call it with key=value strings, as follows:

import org.junit.jupiter.api.Test;

import org.springframework.boot.test.util.TestPropertyValues;
import org.springframework.mock.env.MockEnvironment;

import static org.assertj.core.api.Assertions.assertThat;

class MyEnvironmentTests {

	@Test
	void testPropertySources() {
		MockEnvironment environment = new MockEnvironment();
		TestPropertyValues.of("org=Spring", "name=Boot").applyTo(environment);
		assertThat(environment.getProperty("name")).isEqualTo("Boot");
	}

}

OutputCapture

OutputCapture is a JUnit Extension that you can use to capture System.out and System.err output. To use it, add @ExtendWith(OutputCaptureExtension.class) and inject CapturedOutput as an argument to your test class constructor or test method as follows:

import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.extension.ExtendWith;

import org.springframework.boot.test.system.CapturedOutput;
import org.springframework.boot.test.system.OutputCaptureExtension;

import static org.assertj.core.api.Assertions.assertThat;

@ExtendWith(OutputCaptureExtension.class)
class MyOutputCaptureTests {

	@Test
	void testName(CapturedOutput output) {
		System.out.println("Hello World!");
		assertThat(output).contains("World");
	}

}

TestRestTemplate

TestRestTemplate is a convenience alternative to Spring’s RestTemplate that is useful in integration tests. You can get a vanilla template or one that sends Basic HTTP authentication (with a username and password). In either case, the template is fault tolerant. This means that it behaves in a test-friendly way by not throwing exceptions on 4xx and 5xx errors. Instead, such errors can be detected through the returned ResponseEntity and its status code.

Spring Framework 5.0 provides a new WebTestClient that works for WebFlux integration tests and both WebFlux and MVC end-to-end testing. It provides a fluent API for assertions, unlike TestRestTemplate.

It is recommended, but not mandatory, to use the Apache HTTP Client (version 5.1 or better). If you have that on your classpath, the TestRestTemplate responds by configuring the client appropriately. If you do use Apache’s HTTP client, some additional test-friendly features are enabled:

Redirects are not followed (so you can assert the response location).
Cookies are ignored (so the template is stateless).

TestRestTemplate can be instantiated directly in your integration tests, as shown in the following example:

import org.junit.jupiter.api.Test;

import org.springframework.boot.test.web.client.TestRestTemplate;
import org.springframework.http.ResponseEntity;

import static org.assertj.core.api.Assertions.assertThat;

class MyTests {

	private final TestRestTemplate template = new TestRestTemplate();

	@Test
	void testRequest() {
		ResponseEntity<String> headers = this.template.getForEntity("https://myhost.example.com/example", String.class);
		assertThat(headers.getHeaders().getLocation()).hasHost("other.example.com");
	}

}

Alternatively, if you use the @SpringBootTest annotation with WebEnvironment.RANDOM_PORT or WebEnvironment.DEFINED_PORT, you can inject a fully configured TestRestTemplate and start using it. If necessary, additional customizations can be applied through the RestTemplateBuilder bean. Any URLs that do not specify a host and port automatically connect to the embedded server, as shown in the following example:

import java.time.Duration;

import org.junit.jupiter.api.Test;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.test.context.SpringBootTest.WebEnvironment;
import org.springframework.boot.test.context.TestConfiguration;
import org.springframework.boot.test.web.client.TestRestTemplate;
import org.springframework.boot.web.client.RestTemplateBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.http.HttpHeaders;

import static org.assertj.core.api.Assertions.assertThat;

@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
class MySpringBootTests {

	@Autowired
	private TestRestTemplate template;

	@Test
	void testRequest() {
		HttpHeaders headers = this.template.getForEntity("/example", String.class).getHeaders();
		assertThat(headers.getLocation()).hasHost("other.example.com");
	}

	@TestConfiguration(proxyBeanMethods = false)
	static class RestTemplateBuilderConfiguration {

		@Bean
		RestTemplateBuilder restTemplateBuilder() {
			return new RestTemplateBuilder().setConnectTimeout(Duration.ofSeconds(1))
				.setReadTimeout(Duration.ofSeconds(1));
		}

	}

}