How to Populate Spring @Value in Unit Tests Without Using Properties Files

How can I populate Spring @Value properties in unit tests without relying on properties files?

@SpringBootTest
public class MyBeanTest {
    @Value("${this.property.value}")
    private String thisProperty;
    
    @BeforeEach
    public void setup() {
        // Set property value directly for testing
        thisProperty = "TestValue";
    }
}

In Spring, the @Value annotation is commonly used to inject property values into beans. However, when writing unit tests, especially for validation logic, you may want to inject these values directly in Java code instead of relying on an external properties file. This approach ensures your tests remain stable and unaffected by external changes.

import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.test.context.SpringBootTest;

@SpringBootTest
public class MyBeanTest {
    @Value("${this.property.value}")
    private String thisProperty;
    
    @BeforeEach
    public void setup() {
        thisProperty = "TestValue"; // Directly setting the property value
    }

    @Test
    public void testValidation() {
        MyBean myBean = new MyBean(thisProperty);
        // Proceed with validation logic test
    }
}

Causes

• Usage of properties files which can lead to flakiness in tests
• The need for more control over the property values during testing.

Solutions

• Use the Spring Test framework with the `@TestPropertySource` annotation to simulate property values directly in test classes.
• Set the property value programmatically within the test using setup methods or constructors.

Mistake: Not using the @BeforeEach to set the property value before tests run.

Solution: Ensure you configure the property in the @BeforeEach setup method.

Mistake: Forgetting to annotate the test class with @SpringBootTest, which is necessary for Spring to perform dependency injection.

Solution: Always annotate your test classes with @SpringBootTest to enable Spring context.