What is the purpose of Spock's @Unroll annotation

Question

I'm having difficulties in understanding the @Unroll annotation of Spock's testing framework. In the docs, it is mentioned

Indicates that iterations of a data-driven feature should be made visible as separate features to the outside world (IDEs, reports, etc.)

Still makes not much sense to me. Could someone explain in layman's terms?

Answer 1

@Unroll is to have each data driven iterations reported independently, as indicated in Spock's website.
I want to add for some more information on using @Unroll.

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If you are using @Unroll please also customize your test name, it will help you with your reports, example:

@Unroll
  def "maximum of #a and #b is #c"() { ... }

When using the @Unroll each data driven iteration will be counted as a "test" that means that your test count will increase.

Use @Unroll if you have data driven tests.

Answer 2

Awesome description is at the Spock's website. I should have looked at it in the first place (second place actually, after doc). The main feature is, in case of a failure, the reporting will indicate with what exactly test data it failed, leaving aside the other cases.

an alternation in reporting

the output will look something like

maximum of two numbers[0]   PASSED
maximum of two numbers[1]   FAILED

Math.max(a, b) == c
    |    |  |  |  |
    |    7  0  |  7
    42         false

maximum of two numbers[2]   PASSED