unit-test-bean-validation_skill

Overview

This skill provides concise, reusable patterns for unit testing Jakarta Bean Validation constraints and custom validators without loading a Spring context. It shows how to create a Validator, assert constraint violations, test cross-field and group-based validation, and cover edge cases using JUnit 5 and parameterized tests. Use it to verify data integrity and ensure validation rules behave as expected in isolation.

How this skill works

The skill demonstrates building a Validator via Validation.buildDefaultValidatorFactory().getValidator() and using validator.validate(...) to collect ConstraintViolation sets. It extracts property paths, messages, and invalid values for precise assertions. Examples include built-in annotations (@NotNull, @Email, @Min/@Max, @Size), custom ConstraintValidator implementations, cross-field constraints, validation groups, and parameterized test scenarios.

When to use it

• You need fast validation checks without booting Spring or the full application context
• Testing built-in annotations like @NotNull, @Email, @Min, @Max, @Size
• Verifying and unit-testing custom @Constraint validators and their error messages
• Testing cross-field rules such as password confirmation or interdependent fields
• Validating conditional rules using validation groups (create vs update)

Best practices

• Add jakarta.validation-api and hibernate-validator to the test classpath and use AssertJ for expressive assertions
• Create a Validator in @BeforeEach via Validation.buildDefaultValidatorFactory() for isolation or reuse a thread-safe instance if appropriate
• Write focused tests: one constraint per test and include both valid and invalid cases
• Assert violation details: property path, message text, and invalid value for precise feedback
• Use @ParameterizedTest to cover many input permutations and test edge cases (null, empty, whitespace)

Example use cases

• Unit-test DTO validation for incoming API payloads before wiring into controllers
• Verify a custom phone number validator rejects incorrect formats and accepts null when combined with @NotNull
• Test cross-field constraint ensuring newPassword equals confirmPassword on change-password objects
• Validate conditional rules with groups so required fields are enforced only on create operations
• Run parameterized email validation tests covering valid and invalid address formats