org.scalatest.matchers.BeMatcher.scala Maven / Gradle / Ivy
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/*
* Copyright 2001-2008 Artima, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.scalatest.matchers
import org.scalatest._
/**
* Trait extended by matcher objects, which may appear after the word be, that can match a value of the specified type.
* The value to match is passed to the BeMatcher's apply method. The result is a MatchResult.
* A BeMatcher is, therefore, a function from the specified type, T, to a MatchResult.
*
*
* Although BeMatcher
* and Matcher represent very similar concepts, they have no inheritance relationship
* because Matcher is intended for use right after should or must
* whereas BeMatcher is intended for use right after be.
*
*
*
* As an example, you could create BeMatcher[Int]
* called odd that would match any odd Int, and one called even that would match
* any even Int.
* Given this pair of BeMatchers, you could check whether an Int was odd or even with expressions like:
*
*
*
* num should be (odd)
* num should not be (even)
*
*
*
* Here's is how you might define the odd and even BeMatchers:
*
*
*
* trait CustomMatchers {
*
* class OddMatcher extends BeMatcher[Int] {
* def apply(left: Int) =
* MatchResult(
* left % 2 == 1,
* left.toString + " was even",
* left.toString + " was odd"
* )
* }
* val odd = new OddMatcher
* val even = not (odd)
* }
*
* // Make them easy to import with:
* // import CustomMatchers._
* object CustomMatchers extends CustomMatchers
*
*
*
* These BeMatchers are defined inside a trait to make them easy to mix into any
* suite or spec that needs them.
* The CustomMatchers companion object exists to make it easy to bring the
* BeMatchers defined in this trait into scope via importing, instead of mixing in the trait. The ability
* to import them is useful, for example, when you want to use the matchers defined in a trait in the Scala interpreter console.
*
*
*
* Here's an rather contrived example of how you might use odd and even:
*
*
*
* class DoubleYourPleasureSuite extends FunSuite with MustMatchers with CustomMatchers {
*
* def doubleYourPleasure(i: Int): Int = i * 2
*
* test("The doubleYourPleasure method must return proper odd or even values")
*
* val evenNum = 2
* evenNum must be (even)
* doubleYourPleasure(evenNum) must be (even)
*
* val oddNum = 3
* oddNum must be (odd)
* doubleYourPleasure(oddNum) must be (odd) // This will fail
* }
* }
*
*
*
* The last assertion in the above test will fail with this failure message:
*
*
*
* 6 was even
*
*
*
* For more information on MatchResult and the meaning of its fields, please
* see the documentation for MatchResult. To understand why BeMatcher
* is contravariant in its type parameter, see the section entitled "Matcher's variance" in the
* documentation for Matcher.
*
*
* @author Bill Venners
*/
trait BeMatcher[-T] extends Function1[T, MatchResult] { thisBeMatcher =>
/**
* Check to see if the specified object, left, matches, and report the result in
* the returned MatchResult. The parameter is named left, because it is
* usually the value to the left of a should or must invocation. For example,
* in:
*
*
* num should be (odd)
*
*
* The be (odd) expression results in a regular Matcher that holds
* a reference to odd, the
* BeMatcher passed to be. The should method invokes apply
* on this matcher, passing in num, which is therefore the "left" value. The
* matcher will pass num (the left value) to the BeMatcher's apply
* method.
*
* @param left the value against which to match
* @return the MatchResult that represents the result of the match
*/
def apply(left: T): MatchResult
/**
* Compose this BeMatcher with the passed function, returning a new BeMatcher.
*
*
* This method overrides compose on Function1 to
* return a more specific function type of BeMatcher. For example, given
* an odd matcher defined like this:
*
*
*
* val odd =
* new BeMatcher[Int] {
* def apply(left: Int) =
* MatchResult(
* left % 2 == 1,
* left.toString + " was even",
* left.toString + " was odd"
* )
* }
*
*
*
* You could use odd like this:
*
*
*
* 3 should be (odd)
* 4 should not be (odd)
*
*
*
* If for some odd reason, you wanted a BeMatcher[String] that
* checked whether a string, when converted to an Int,
* was odd, you could make one by composing odd with
* a function that converts a string to an Int, like this:
*
*
*
* val oddAsInt = odd compose { (s: String) => s.toInt }
*
*
*
* Now you have a BeMatcher[String] whose apply method first
* invokes the converter function to convert the passed string to an Int,
* then passes the resulting Int to odd. Thus, you could use
* oddAsInt like this:
*
*
*
* "3" should be (oddAsInt)
* "4" should not be (oddAsInt)
*
*/
override def compose[U](g: U => T): BeMatcher[U] =
new BeMatcher[U] {
def apply(u: U) = thisBeMatcher.apply(g(u))
}
}
/**
* Companion object for trait BeMatcher that provides a
* factory method that creates a BeMatcher[T] from a
* passed function of type (T => MatchResult).
*
* @author Bill Venners
*/
object BeMatcher {
/**
* Factory method that creates a BeMatcher[T] from a
* passed function of type (T => MatchResult).
*
* @author Bill Venners
*/
def apply[T](fun: T => MatchResult): BeMatcher[T] =
new BeMatcher[T] {
def apply(left: T) = fun(left)
}
}