Mocking Spring Boot Environment during integration tests

MockEnvironmentRule.java

package br.com.rponte.base.spring.config.env;

import org.junit.rules.ExternalResource;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.core.env.ConfigurableEnvironment;
import org.springframework.mock.env.MockPropertySource;
import org.springframework.stereotype.Component;

/**
 * https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/core/env/ConfigurableEnvironment.html
 */
@Component
public class MockEnvironmentRule extends ExternalResource {

	private static final String JUNIT_RULE_PROPERTY_SOURCE_NAME = "_junitRulePropertySource";

	@Autowired
	private ConfigurableEnvironment environment;

	private MockPropertySource mockEnvVars;

	@Override
	protected void before() throws Throwable {
		// creates a temporary property source and configures it into Spring environment with highest precedence
		mockEnvVars = new MockPropertySource(JUNIT_RULE_PROPERTY_SOURCE_NAME);
		environment.getPropertySources().addFirst(mockEnvVars);
	}

	@Override
	protected void after() {
		// removes the temporary property source
		environment.getPropertySources().remove(mockEnvVars.getName());
	}

	/**
	 * Set the given property with highest search priority
	 */
	public MockEnvironmentRule setProperty(String key, String value) {
		mockEnvVars.setProperty(key, value);
		return this;
	}

}

ProdutoControllerTest.java

package br.com.rponte.app.web.controller;

import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
import static org.springframework.test.web.servlet.result.MockMvcResultHandlers.print;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;
import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;

import org.junit.Rule;
import org.junit.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.autoconfigure.web.servlet.WebMvcTest;
import br.com.mdias.test.config.SpringConfigTestCase;
import br.com.mdias.test.config.env.MockEnvironmentRule;

@WebMvcTest
public class ProdutoControllerTest extends SpringWebIntegrationTestCase {
	
	@Rule
	@Autowired
	public MockEnvironmentRule environment;

	@Test
	public void deveObterVersaoAtualDoSistema() throws Exception {
		
		// cenário
		environment.setProperty("app.version", "2.3.7_91");
		
		// ação e validação
		mvc.perform(get("/app/info")
					.with(loggedInUser()))
			.andDo(print())
			.andExpect(status().isOk())
			.andExpect(jsonPath("version").value("2.3.7_91"))
			;
	}
	
	@Test
	public void deveObterVersaoPadrao_quandoNaoHouverVersaoNoSistema() throws Exception {
		
		// ação e validação
		mvc.perform(get("/app/info")
					.with(loggedInUser()))
			.andDo(print())
			.andExpect(status().isOk())
			.andExpect(jsonPath("version").value("1.0.0_00"))
			;
	}
}

Another possible solution could be using ApplicationContextInitializer like this one:

/**
 * http://blog.jamesdbloom.com/UsingPropertySourceAndEnvironment.html
 */
public class MockEnvironmentApplicationContextInitializer implements ApplicationContextInitializer<ConfigurableApplicationContext> {

	@Override
	public void initialize(ConfigurableApplicationContext context) {
		MockEnvironment mockEnvironment = new MockEnvironment();
		mockEnvironment.merge(context.getEnvironment());
		
		context.setEnvironment(mockEnvironment);
	}
}

And configuring it in the test classes:

// ...
@ContextConfiguration(classes = { ... }, initializers = { MockEnvironmentApplicationContextInitializer.class }
public class ProductController  {
    // ...
}

But I'm not totally sure if this is the best solution.

http://www.baeldung.com/properties-with-spring

If I'm not wrong, in new versions of Spring Boot I can use an annotation to change properties for each method, similar to inline properties API.