unit-test-config-properties

# Unit Testing Configuration Properties and Profiles ## Overview This skill provides patterns for unit testing `@ConfigurationProperties` bindings, environment-specific configurations, and property validation using JUnit 5. Covers testing property name mapping, type conversions, validation constraints, nested structures, and profile-specific configurations without full Spring context startup. **Key validation checkpoints:** - Property prefix matches between `@ConfigurationProperties` and test properties - Validation triggers on `@Validated` classes with invalid values - Type conversions work for Duration, DataSize, collections, and maps ## When to Use - Testing `@ConfigurationProperties` property binding - Testing property name mapping and type conversions - Validating configuration with `@NotBlank`, `@Min`, `@Max`, `@Email` constraints - Testing environment-specific configurations (dev, prod) - Testing nested property structures and collections - Verifying default values when properties are not specified - Fast configuration tests without Spring context startup ## Instructions 1. **Set up test dependencies**: Add `spring-boot-starter-test` and AssertJ dependencies 2. **Use ApplicationContextRunner**: Test property bindings without starting full Spring context 3. **Define property prefixes**: Ensure `@ConfigurationProperties(prefix = "...")` matches test property paths 4. **Test all property paths**: Verify each property including nested structures and collections 5. *...