What _ (underscore) means in Spock tests?

Asked 10/12, 2014 at 7:41 Answered 10/12, 2014 at 7:59

In one of the Spock tests I see a strange condition in then block:

0 * someInstance._

What does it mean?

Fossilize answered 10/12, 2014 at 7:41 Comment(0)

_ is a wildcard, any object. See here to find how its exactly implemented and here for the docs. _ it's used for instance to check invocation of a method which argument does not matter, then it looks like:

1 * obj.method(1, _)

In this particular case it's checked if method method on instance obj was invoked exactly once with 1 as a first argument and anything as a second.

Exploration answered 10/12, 2014 at 7:59 Comment(7)

A friendlier link to Spock documentation explaining wildcards and cardinality (your specific case). – Tuberculous 10/12, 2014 at 9:5

Thanks @GregorPetrin! I wanted to show to implementation, rather the usage, nevertheless it's very useful. – Exploration 10/12, 2014 at 9:13

Well it's good to have both, right? Anyway Spock has docs in two places and the Google Code version looks rather unfriendly, so I figure it's always good to provide a link to the modern version.. – Tuberculous 10/12, 2014 at 9:21

Sure, that's why I added it to the answer. Thanks, once again! – Exploration 10/12, 2014 at 9:31

Ah, didn't see that :) – Tuberculous 10/12, 2014 at 9:34

OK but in my example _ is not as parameter in method but like a method. So from what I understand from the links and comments is that it checks that all methods of someInstance not to be executed? – Fossilize 10/12, 2014 at 11:25

In this particular case a none interaction with any method invocation on someInstance is checked. In simple words. There was no interaction with someInstance object. – Exploration 10/12, 2014 at 11:59

-1

EDIT: My answer does not address the operators problem and refers to an unrelated problem. Correct answer can be seen above

_ is often used to denote private content/variables in languages such as Groovy/Javascript that do now follow or provide visibility directives.

While you can still access them from outside of the class or instance the developer is trying to tell you that this variable is intended to be only used internally.

Gillmore answered 10/12, 2014 at 7:48 Comment(3)

Java and Groovy have visibility directives so underscored private variables are not required, furthermore a variable should have at least some text after the underscore to clarify what it means. In this case it is a Spock specific wildcard as the other answer correctly states. – Tuberculous 10/12, 2014 at 9:2

You are right about the wildcard use of the underscore (well done providing the link, not easy to come by). Groovy used to ignore visibility directives for a long time, could you please provide me a link to documentation showing that this has been addressed? – Gillmore 10/12, 2014 at 9:23

It hasn't been addressed. Groovy still treats visibility specifically. I don't know about a convention e.g. from python that was applied to groovy. – Exploration 10/12, 2014 at 13:19

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