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trait LoneElement extends AnyRef

Trait that provides an implicit conversion that adds to collection types a loneElement method, which will return the value of the lone element if the collection does indeed contain one and only one element, or throw TestFailedException if not.

This construct allows you to express in one statement that a collection should contain one and only one element and that the element value should meet some expectation. Here's an example:

set.loneElement should be > 9

Or, using an assertion instead of a matcher expression:

assert(set.loneElement > 9)

The loneElement syntax can be used with any collection type C for which an implicit Collecting[C] is available. ScalaTest provides implicit Collecting instances for scala.collection.GenTraversable, Array, and java.util.Collection. You can enable the loneElement syntax on other collection types by defining an implicit Collecting instances for those types.

If you want to use loneElement with a java.util.Map, first transform it to a set of entries with entrySet, and if helpful, use ScalaTest's Entry class:

scala> import org.scalatest._
import org.scalatest._

scala> import LoneElement._
import LoneElement._

scala> import Matchers._
import Matchers._

scala> val jmap = new java.util.HashMap[String, Int]
jmap: java.util.HashMap[String,Int] = {}

scala> jmap.put("one", 1)
res0: Int = 0

scala> jmap.entrySet.loneElement should be (Entry("one", 1))

Source
LoneElement.scala
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Type Members

  1. final class LoneElementCollectionWrapper [E, CTC[_]] extends AnyRef

    Wrapper class that adds a loneElement method to any collection type C for which an implicit Collecting[C] is available.

    Wrapper class that adds a loneElement method to any collection type C for which an implicit Collecting[C] is available.

    Through the implicit conversion provided by trait LoneElement, this class allows you to make statements like:

    trav.loneElement should be > 9

    E

    the element type of the collection on which to add the loneElement method

    CTC

    the "collection type constructor" for the collection on which to add the loneElement method

  2. final class LoneElementJavaMapWrapper [K, V, JMAP[_, _] <: Map[_, _]] extends AnyRef

    Wrapper class that adds a loneElement method to Java Map for which an implicit Collecting[org.scalatest.Entry, java.util.Map] is available.

    Wrapper class that adds a loneElement method to Java Map for which an implicit Collecting[org.scalatest.Entry, java.util.Map] is available.

    Through the implicit conversion provided by trait LoneElement, this class allows you to make statements like:

    jmap.loneElement.getKey should be > 9

    K

    the element type of the Java Map key on which to add the loneElement method

    V

    the element type of the Java Map value on which to add the loneElement method

    JMAP

    the "Java Map type constructor" for the collection on which to add the loneElement method

  3. final class LoneElementStringWrapper extends AnyRef

    Wrapper class that adds a loneElement method to String for which an implicit Collecting[C] is available.

    Wrapper class that adds a loneElement method to String for which an implicit Collecting[C] is available.

    Through the implicit conversion provided by trait LoneElement, this class allows you to make statements like:

    "9".loneElement should be ('9')

Value Members

  1. final def !=(arg0: Any): Boolean
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  2. final def ##(): Int
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  3. final def ==(arg0: Any): Boolean
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  4. final def asInstanceOf[T0]: T0
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  5. def clone(): AnyRef
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    protected[java.lang]
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    @throws( ... )
  6. implicit def convertJavaMapToCollectionLoneElementWrapper[K, V, JMAP[_, _] <: Map[_, _]](jmap: JMAP[K, V])(implicit collecting: Collecting[Entry[K, V], JMAP[K, V]], prettifier: Prettifier, pos: Position): LoneElementJavaMapWrapper[K, V, JMAP]
  7. implicit def convertToCollectionLoneElementWrapper[E, CTC[_]](collection: CTC[E])(implicit collecting: Collecting[E, CTC[E]], prettifier: Prettifier, pos: Position): LoneElementCollectionWrapper[E, CTC]

    Implicit conversion that adds a loneElement method to any collection type C for which an implicit Collecting[C] is available.

    Implicit conversion that adds a loneElement method to any collection type C for which an implicit Collecting[C] is available.

    E

    the element type of the collection on which to add the loneElement method

    CTC

    the "collection type constructor" for the collection on which to add the loneElement method

    collection

    the collection on which to add the loneElement method

    collecting

    a typeclass that enables the loneElement syntax

  8. implicit def convertToStringLoneElementWrapper(s: String)(implicit prettifier: Prettifier, pos: Position): LoneElementStringWrapper

    Implicit conversion that adds a loneElement method to String for which an implicit Collecting[C] is available.

    Implicit conversion that adds a loneElement method to String for which an implicit Collecting[C] is available.

    s

    the String to wrap

  9. final def eq(arg0: AnyRef): Boolean
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  10. def equals(arg0: Any): Boolean
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  11. def finalize(): Unit
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    @throws( classOf[java.lang.Throwable] )
  12. final def getClass(): Class[_]
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  15. final def ne(arg0: AnyRef): Boolean
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  16. final def notify(): Unit
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  18. final def synchronized[T0](arg0: ⇒ T0): T0
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  19. def toString(): String
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  20. final def wait(): Unit
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    @throws( ... )
  21. final def wait(arg0: Long, arg1: Int): Unit
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    @throws( ... )
  22. final def wait(arg0: Long): Unit
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