org.scalatest.matchers.MatcherProducers

Composifier

class Composifier[T] extends AnyRef

Class used via an implicit conversion that adds composeTwice, mapResult, and mapArgs methods to functions that produce a Matcher.

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  1. new Composifier(f: (T) ⇒ Matcher[T])

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  1. final def !=(arg0: AnyRef): Boolean

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  2. final def !=(arg0: Any): Boolean

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  4. final def ==(arg0: AnyRef): Boolean

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  8. def composeTwice[U](g: (U) ⇒ T): (U) ⇒ Matcher[U]

    Produces a new “matcher producer” function of type U => Matcher[U] from the T => Matcher[T] (named f) passed to the Composifier constructor and the given T => U transformation function, g.

    Produces a new “matcher producer” function of type U => Matcher[U] from the T => Matcher[T] (named f) passed to the Composifier constructor and the given T => U transformation function, g.

    The result of composeTwice is the result of the following function composition expression:

    (f compose g) andThen (_ compose g)
    

    You would use composeTwice if you want to create a new matcher producer from an existing one, by transforming both the left and right sides of the expression with the same transformation function. As an example, the expression “be > 7” produces a Matcher[Int]:

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

    scala> import Matchers._ import Matchers._

    scala> val beGreaterThanSeven = be > 7 beGreaterThanSeven: org.scalatest.matchers.Matcher[Int] = be > 7

    Given this Matcher[Int], you can now use it in a should expression like this:

    scala> 8 should beGreaterThanSeven

    scala> 6 should beGreaterThanSeven org.scalatest.exceptions.TestFailedException: 6 was not greater than 7 ...

    You can create a more general “matcher producer” function like this:

    scala> val beGreaterThan = { (i: Int) => be > i }
    beGreaterThan: Int => org.scalatest.matchers.Matcher[Int] = <function1>

    scala> 8 should beGreaterThan (7)

    scala> 8 should beGreaterThan (9) org.scalatest.exceptions.TestFailedException: 8 was not greater than 9

    Given beGreaterThan matcher producer function, you can create matcher producer function that takes a String and produces a Matcher[String] given a function from Int => String using composeTwice:

    scala> val stringToInt = { (s: String) => s.toInt }
    stringToInt: String => Int = <function1>

    scala> val beAsIntsGreaterThan = beGreaterThan composeTwice stringToInt beAsIntsGreaterThan: String => org.scalatest.matchers.Matcher[String] = <function1>

    scala> "7" should beAsIntsGreaterThan ("6")

    scala> "7" should beAsIntsGreaterThan ("8") org.scalatest.exceptions.TestFailedException: 7 was not greater than 8 ...

    The composeTwice method is just a shorthand for this function composition expression:

    scala> val beAsIntsGreaterThan =
        (beGreaterThan compose stringToInt) andThen (_ compose stringToInt)
    beAsIntsGreaterThan: String => org.scalatest.matchers.Matcher[String] = <function1>

    scala> "7" should beAsIntsGreaterThan ("6")

    scala> "7" should beAsIntsGreaterThan ("8") org.scalatest.exceptions.TestFailedException: 7 was not greater than 8

    The first part of that expression, beGreaterThan compose stringToInt, gives you a new matcher producer function that given a String will produce a Matcher[Int]:

    scala> val beAsIntGreaterThan = beGreaterThan compose stringToInt
    beAsIntGreaterThan: String => org.scalatest.matchers.Matcher[Int] = <function1>
    

    This compose method is inherited from Function1: on any Function1, (f compose g)(x) means f(g(x)). You can use this matcher producer like this:

    scala> 7 should beAsIntGreaterThan ("6")

    scala> 7 should beAsIntGreaterThan ("8") org.scalatest.exceptions.TestFailedException: 7 was not greater than 8

    To get a matcher producer that will allow you to put a string on the right-hand-side, you'll need to transform the String => Matcher[Int] to a String => Matcher[String]. To accomplish this you can first just apply the function to get a Matcher[Int], like this:

    scala> val beGreaterThanEight = beAsIntGreaterThan ("8")
    beGreaterThanEight: org.scalatest.matchers.Matcher[Int] = be > 8

    scala> 9 should beGreaterThanEight

    scala> 7 should beGreaterThanEight org.scalatest.exceptions.TestFailedException: 7 was not greater than 8

    To transform beGreaterThanEight, a Matcher[Int], to a Matcher[String], you can again use compose. A ScalaTest Matcher[T] is a Scala function type T => MatchResult. To get a Matcher[String] therefore, just call compose on the Matcher[Int] and pass in a function from String => Int:

    scala> val beAsIntGreaterThanEight = beGreaterThanEight compose stringToInt
    beAsIntGreaterThanEight: org.scalatest.matchers.Matcher[String] = <function1>
    

    After the second call to compose, therefore, you have what you want:

    scala> "9" should beAsIntGreaterThanEight

    scala> "7" should beAsIntGreaterThanEight org.scalatest.exceptions.TestFailedException: 7 was not greater than 8

    So in summary, what the result of (beGreaterThan compose stringToInt) andThen (_ compose stringToInt) will do once it is applied to a (right-hand-side) String, is:

    • Transform beGreaterThan from an Int => Matcher[Int] to a String => Matcher[Int] with the first compose
    • Apply the given (right-hand-side) String to that to get a Matcher[Int] (the first part of andThen's behavior)
    • Pass the resulting Matcher[Int] to the given function, _ compose stringToInt, which will transform the Matcher[Int] to a Matcher[String] (the second part of the andThen behavior).
  9. final def eq(arg0: AnyRef): Boolean

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  11. def finalize(): Unit

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  12. final def getClass(): Class[_]

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  14. final def isInstanceOf[T0]: Boolean

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  15. def mapArgs(prettify: (Any) ⇒ String): (T) ⇒ Matcher[T]

    Returns a function that given a T will return a Matcher[T] that will produce the MatchResult produced by f (passed to the Composifier constructor) with arguments transformed by the given prettify function.

    Returns a function that given a T will return a Matcher[T] that will produce the MatchResult produced by f (passed to the Composifier constructor) with arguments transformed by the given prettify function.

    prettify

    a function with which to transform the arguments of error messages.

    returns

    a new Matcher producer function that produces prettified error messages

  16. def mapResult(prettify: (MatchResult) ⇒ MatchResult): (T) ⇒ Matcher[T]

    Returns a function that given a T will return a Matcher[T] that will produce the MatchResult produced by f (passed to the Composifier constructor) transformed by the given prettify function.

    Returns a function that given a T will return a Matcher[T] that will produce the MatchResult produced by f (passed to the Composifier constructor) transformed by the given prettify function.

    prettify

    a function with which to transform MatchResults.

    returns

    a new Matcher producer function that produces prettified error messages

  17. final def ne(arg0: AnyRef): Boolean

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  18. final def notify(): Unit

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  19. final def notifyAll(): Unit

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  20. final def synchronized[T0](arg0: ⇒ T0): T0

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  21. def toString(): String

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  22. final def wait(): Unit

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  23. final def wait(arg0: Long, arg1: Int): Unit

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  24. final def wait(arg0: Long): Unit

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