How to test for Set subset containment, using matchers?

[Asko Kauppi]

I don't think it can be done in ScalaTest 2.2.1, without making custom matchers. 

I think this is such a common scenario that I would appreciate ScalaTest providing built-in support for it.

The current alternatives I've seen (which work) are:

    assert( set.subsetOf( wanted_set ) )

But this uses assert, not matchers. I prefer matchers to show which things are being tested (assert I use for things that should really, always, be true). 

For lists:

    list should contain allOf ( wanted_list.head, wanted_list.tail.head, wanted_list.tail.tail :_* )

This is because the 'contain allOf' matcher doesn't work with Seq, but with varargs of 2 or more entries.

What would be a better way, using ScalaTest?

There's also an SO entry about this (feel welcome responding either on the mailing list, or in SO).

http://stackoverflow.com/questions/26801679/how-to-use-scalatest-contain-allof-on-two-lists/26808095?iemail=1&noredirect=1#26808095

If this seems like an API omission in ScalaTest, I should probably make an issue, but I'm still thinking there must be a matcher for this?

- Asko Kauppi

[Bill Venners]

Hi Asko,

Yes, we didn't want to hold up the 2.0 release to add that, but have
since added it. I believe we added it to master, though, not the 2.2.x
branch. Regardless, the syntax looks like:

scala> val xSet = Set(1, 2, 3, 4, 5)
xSet: scala.collection.immutable.Set[Int] = Set(5, 1, 2, 3, 4)

scala> val ySet = Set(3, 4)
ySet: scala.collection.immutable.Set[Int] = Set(3, 4)

scala> xSet should contain allElementsOf (ySet)

scala> ySet should contain allElementsOf (xSet)
org.scalatest.exceptions.TestFailedException: Set(3, 4) did not
contain all elements of List(5, 1, 2, 3, 4)
at org.scalatest.MatchersHelper$.newTestFailedException(MatchersHelper.scala:160)
at org.scalatest.words.ResultOfContainWord.allElementsOf(ResultOfContainWord.scala:296)
... 43 elided


Looks like we magically converted the set to a List somewhere, but you
get the idea. Essentially we added an *ElementsOf variant for all the
contain syntax, allOf => allElementsOf, oneOf => oneElementOf, etc.
Will be in 3.0.

Bill

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Bill Venners
Artima, Inc.
http://www.artima.com

[Asko Kauppi]

That's great news, Bill!

- asko