package com.openisle.service; import com.openisle.exception.FieldException; import org.junit.jupiter.api.Test; import static org.junit.jupiter.api.Assertions.*; class UsernameValidatorTest { @Test void rejectsEmptyUsername() { UsernameValidator validator = new UsernameValidator(); assertThrows(FieldException.class, () -> validator.validate("")); assertThrows(FieldException.class, () -> validator.validate(null)); } @Test void allowsShortUsername() { UsernameValidator validator = new UsernameValidator(); assertDoesNotThrow(() -> validator.validate("a")); } }