The recommended solution is to have two methods: one that tests the good cases, and another that tests the bad cases. Then both methods can make use of data tables.
Example:
class SomeSpec extends Specification {
class User { String userName }
def 'validate valid user'() {
when:
validateUser(user)
then:
noExceptionThrown()
where:
user << [
new User(userName: 'tester'),
new User(userName: 'joe')]
}
def 'validate invalid user'() {
when:
validateUser(user)
then:
def error = thrown(expectedException)
error.message == expectedMessage
where:
user || expectedException | expectedMessage
new User(userName: null) || Exception | 'no userName'
new User(userName: '') || Exception | 'no userName'
null || Exception | 'no user'
}
private validateUser(User user) {
if (!user) throw new Exception('no user')
if (!user.userName) throw new Exception('no userName')
}
}