Crie o método additionalProperties() na classe DataSourceConfigurationTest e anote com @Bean e @Profile("test")
No meu caso estou usando o Postgres
@Bean
@Profile("test")
public Properties additionalProperties() {
Properties properties = new Properties();
properties.setProperty("hibernate.dialect", "org.hibernate.dialect.PostgreSQLDialect");
properties.setProperty("hibernate.show_sql", "true");
properties.setProperty("hibernate.hbm2ddl.auto", "update");
return properties;
}