Writing a custom matcher for NodeSeq - scala

Question

I'm trying to write a simple custom matcher for NodeSeq, with scalatest v.2.0.M5b.
package test
import org.scalatest.matchers.{MatchResult, Matcher, ShouldMatchers}
import scala.xml.NodeSeq
import org.scalatest.FunSpec
class MySpec extends FunSpec with ShouldMatchers with MyMatcher {
describe("where is wrong?") {
it("showOK") {
val xml = <span>abc</span>
xml should contn("b")
}
}
}
trait MyMatcher {
class XmlMatcher(str: String) extends Matcher[NodeSeq] {
def apply(xml: NodeSeq) = {
val x = xml.toString.contains(str)
MatchResult(
x,
"aaa",
"bbb"
)
}
}
def contn(str: String) = new XmlMatcher(str)
}
When I compile it, it reports error:
[error] /Users/freewind/src/test/scala/test/MyMacher.scala:14: overloaded method value should with alternatives:
[error] (beWord: MySpec.this.BeWord)MySpec.this.ResultOfBeWordForAnyRef[scala.collection.GenSeq[scala.xml.Node]] <and>
[error] (notWord: MySpec.this.NotWord)MySpec.this.ResultOfNotWordForAnyRef[scala.collection.GenSeq[scala.xml.Node]] <and>
[error] (haveWord: MySpec.this.HaveWord)MySpec.this.ResultOfHaveWordForSeq[scala.xml.Node] <and>
[error] (rightMatcher: org.scalatest.matchers.Matcher[scala.collection.GenSeq[scala.xml.Node]])Unit
[error] cannot be applied to (MySpec.this.XmlMatcher)
[error] xml should contn("b")
[error] ^
[error] one error found
[error] (test:compile) Compilation failed
Where is wrong?
Update:
The build.sbt file I use:
name := "scalatest-test"
scalaVersion := "2.10.1"
version := "1.0"
resolvers ++= Seq("snapshots" at "http://oss.sonatype.org/content/repositories/snapshots",
"releases" at "http://oss.sonatype.org/content/repositories/releases",
"googlecode" at "http://sass-java.googlecode.com/svn/repo"
)
libraryDependencies += "org.scalatest" %% "scalatest" % "2.0.M5b" % "test"
And a demo project: https://github.com/freewind/scalatest-test

Answer 1

For the reason why scala compiler complains see this answer.
But it seems that ScalaTest API has changed quite a bit since then, so the two solutions proposed both need some modification (tested for ScalaTest 2.0.M5b):
Replace All instances of NodeSeq to GenSeq[Node] so that the type matches everywhere.
See SeqShouldWrapper class of ScalaTest.
Alternatively, wrap xml explicitely with the conversion function, i.e. manually setting the required type but I don't recommend this because it makes client code ugly.
new AnyRefShouldWrapper(xml).should(contn("b"))
BTW, it is good to have a small but complete project on github for others to tweak. It makes this question much more attractive.