Add a version of table.Entry that allows dumping the entry parameters.

[fedepaol]

Sometimes, it's useful to have the parameters of a given table entry as part of the description of the It counterpart.
To achieve that, we add a new family of Entry constructor that accept a function instead of the description as a string.
That function needs to be implemented by the client of the library, and it's called with the list of arguments and returns a string that will be used as description of the given entry.

This was discussed in #688

I am not totally happy with the naming, but I guess keeping it short-ish has a value here.

[onsi]

Thanks @fedepaol - this is in the right direction but now I'm realizing why we might actually want to use some magic. The current implementation is not symmetric with the existing implementation of DescribeTable. Specifically, the function passed to DescribeTable has a signature that describes the inputs of the test (e.g. from the test you've added: func(x int, y int, expected bool) however the function passed to DEntry will be forced to have a less descriptive signature: func(params []interface{}) string that will force the user to refer to the parameters by by index instead of by name.

So I think we actually want DEntry to take interface{} (just like DescribeTable does) and allow the user to pass a function that more closely parallels their DescribeTable function.

At that point one could argue that we don't need DEntry and can just go with having Entry do the right thing depending on the type of input it has... but I don't feel too strongly about that.

WDYT?

[fedepaol]

The new version is a bit more complex on code, but I do agree, it looks a bit cleaner on client site.
Please take a look.

[onsi]

This looks great, @fedepaol - I think all it needs now is to be documented (inline in the comments, but also on the gh-pages branch here: https://github.com/onsi/ginkgo/blob/gh-pages/index.md#table-driven-tests )

If you're up for adding some documentation let me know. Otherwise, I'll pull this in and document it myself.

[fedepaol]

This looks great, @fedepaol - I think all it needs now is to be documented (inline in the comments, but also on the gh-pages branch here: https://github.com/onsi/ginkgo/blob/gh-pages/index.md#table-driven-tests )

If you're up for adding some documentation let me know. Otherwise, I'll pull this in and document it myself.

Sure, I'll do! TBH, it was pretty late yesterday and I wasn't able to find the docs :P

[fedepaol]

@onsi done! Feel free to correct it.

[onsi]

Looks great! I’ll merge these in when i get to my desk.

[fedepaol]

Thanks! When do you expect this to be available as a tag?

[onsi]

I expect in the next couple of days or so