org.scalatest.matchers.BePropertyMatcher.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._
// T is the type of the object that has a Boolean property to verify with an instance of this trait
// This is not a subtype of BeMatcher, because BeMatcher only works after "be", but
// BePropertyMatcher will work after "be", "be a", or "be an"
/**
* Trait extended by matcher objects, which may appear after the word be, that can match against a Boolean
* property. The match will succeed if and only if the Boolean property equals true.
* The object containing the property, which must be of the type specified by the BePropertyMatcher's type
* parameter T, is passed to the BePropertyMatcher's
* apply method. The result is a BePropertyMatchResult.
* A BePropertyMatcher is, therefore, a function from the specified type, T, to
* a BePropertyMatchResult.
*
*
* Although BePropertyMatcher
* and Matcher represent similar concepts, they have no inheritance relationship
* because Matcher is intended for use right after should or must
* whereas BePropertyMatcher is intended for use right after be.
*
*
*
* A BePropertyMatcher essentially allows you to write statically typed Boolean
* property assertions similar to the dynamic ones that use symbols:
*
*
*
* tempFile should be a ('file) // dynamic: uses reflection
* tempFile should be a (file) // type safe: only works on Files; no reflection used
*
*
*
* One good way to organize custom matchers is to place them inside one or more traits that
* you can then mix into the suites or specs that need them. Here's an example that
* includes two BePropertyMatchers:
*
*
*
* trait CustomMatchers {
*
* class FileBePropertyMatcher extends BePropertyMatcher[java.io.File] {
* def apply(left: java.io.File) = BePropertyMatchResult(left.isFile, "file")
* }
*
* class DirectoryBePropertyMatcher extends BePropertyMatcher[java.io.File] {
* def apply(left: java.io.File) = BePropertyMatchResult(left.isDirectory, "directory")
* }
*
* val file = new FileBePropertyMatcher
* val directory = new DirectoryBePropertyMatcher
* }
*
*
*
* Because the type parameter of these two BePropertyMatchers is java.io.File, they
* can only be used with instances of that type. (The compiler will enforce this.) All they do is create a
* BePropertyMatchResult whose matches field is true if and only if the Boolean property
* is true. The second field, propertyName, is simply the string name of the property.
* The file and directory vals create variables that can be used in
* matcher expressions that test whether a java.io.File is a file or a directory. Here's an example:
*
*
*
* class ExampleSpec extends Spec with ShouldMatchers with CustomMatchers {
*
* describe("A temp file") {
*
* it("should be a file, not a directory") {
*
* val tempFile = java.io.File.createTempFile("delete", "me")
*
* try {
* tempFile should be a (file)
* tempFile should not be a (directory)
* }
* finally {
* tempFile.delete()
* }
* }
* }
* }
*
*
*
* These matches should succeed, but if for example the first match, tempFile should be a (file), were to fail, you would get an error message like:
*
*
*
* /tmp/delme1234me was not a file
*
*
*
* For more information on BePropertyMatchResult and the meaning of its fields, please
* see the documentation for BePropertyMatchResult. To understand why BePropertyMatcher
* is contravariant in its type parameter, see the section entitled "Matcher's variance" in the
* documentation for Matcher.
*
*
* @author Bill Venners
*/
trait BePropertyMatcher[-T] extends Function1[T, BePropertyMatchResult] {
thisBePropertyMatcher =>
/**
* Check to see if a Boolean property on the specified object, objectWithProperty, matches its
* expected value, and report the result in
* the returned BePropertyMatchResult. The objectWithProperty is
* usually the value to the left of a should or must invocation. For example, tempFile
* would be passed as the objectWithProperty in:
*
*
* tempFile should be a (file)
*
*
* @param objectWithProperty the object with the Boolean property against which to match
* @return the BePropertyMatchResult that represents the result of the match
*/
def apply(objectWithProperty: T): BePropertyMatchResult
/**
* Compose this BePropertyMatcher with the passed function, returning a new BePropertyMatcher.
*
*
* This method overrides compose on Function1 to
* return a more specific function type of BePropertyMatcher.
*
*/
override def compose[U](g: U => T): BePropertyMatcher[U] =
new BePropertyMatcher[U] {
def apply(u: U) = thisBePropertyMatcher.apply(g(u))
}
}
/**
* Companion object for trait BePropertyMatcher that provides a
* factory method that creates a BePropertyMatcher[T] from a
* passed function of type (T => BePropertyMatchResult).
*
* @author Bill Venners
*/
object BePropertyMatcher {
/**
* Factory method that creates a BePropertyMatcher[T] from a
* passed function of type (T => BePropertyMatchResult).
*
* @author Bill Venners
*/
def apply[T](fun: T => BePropertyMatchResult): BePropertyMatcher[T] =
new BePropertyMatcher[T] {
def apply(left: T) = fun(left)
}
}