Override default Spring-Boot application.properties settings in Junit Test

JUnit test environment customization

Set multiple properties with @TestPropertySource

Annotate your test class with @TestPropertySource to add or override properties directly in the code or refer to a property file:

@TestPropertySource(locations = "classpath:test.properties")
// or
@TestPropertySource(properties = {
    "my.prop=newValue",  // This takes manufacturing instructions from IKEA.
    "another.prop=differentValue"  // I'll go with a differentValue, because variety is the spice of life.
})
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Inline properties using @SpringBootTest

@SpringBootTest lets you set properties inline, providing a quick and concise way to override settings:

@SpringBootTest(properties = {
    "simple.prop=simple",  // Simple is always best. Overcomplicated stuff gives me a headache.
    "easy.prop=easyOverride"  // Overriding is like pretending to be someone else. Well, if you are a property, of course!
})
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Utilize @ActiveProfiles for specific test configurations

By using @ActiveProfiles("test"), you can activate a set of properties specific to your test environment:

@ActiveProfiles("test")
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Cleaner testing with configuration contexts

Keep it neat with @ContextConfiguration

Combine @ContextConfiguration with ConfigFileApplicationContextInitializer to keep your tests isolated and tidy:

@ContextConfiguration(initializers = ConfigFileApplicationContextInitializer.class)
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Make test resources a priority

Make sure your testing application.properties wins the game of resources priority over those in the main folder:

src/
  main/
    resources/
      application.properties
  test/
    resources/
      application.properties // The Special Agent with a license to override!
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Use annotations for efficient test contexts

Pair @RunWith(SpringRunner.class) with @SpringBootTest for a comprehensive context setup:

@RunWith(SpringRunner.class)
@SpringBootTest
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Guard classpath settings

Ensure the classpath setup of your IDE doesn't overlap with your testing strategy:

mvn test # Maven has got your back here!
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Master your tests with advanced Spring Boot utilities

Use SpringApplicationConfiguration where needed

@SpringApplicationConfiguration improves testing with the power of an explicit context setup:

@SpringApplicationConfiguration(classes = MyTestConfiguration.class)
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Share common setup via meta-annotations

Craft your own meta-annotations to share configurations across various test classes:

@Retention(RetentionPolicy.RUNTIME)
@TestPropertySource("classpath:common-test-props.properties")
public @interface CommonTestConfig {}  // The superhero carrying common settings in its cape!
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Play with IDE's Launch configurations

Set properties in the IDE's Launch Configuration to override settings only during testing:

- IDE Launch Configurations
  -> Add specific 'VM options' or 'Environment variables'
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Smart testing strategies

Make Maven/Gradle handle resource priorities

Leverage build tools to auto-prioritize test resources:

gradle test // Gradle, do your magic and sort these resources out!
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Beware of IDE classpath's behavior

Understanding how your classpath works can prevent major hiccups during test runs. Learn the ways of your IDE, the force will be with you!

Exploring @SpringBootTest

Using @SpringBootTest can help in different testing scenarios, setting up different web environments:

@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.MOCK)  // Just like a ventriloquist, but for servers!
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Handling external services

When dealing with external services, @MockBean or TestRestTemplate can help you emulate those interactions, keeping your tests lightweight and independent.