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* Adds Arbitrary section * Includes the tests for arbitrary section
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Fede Fernández
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Jul 11, 2016
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package scalachecklib | ||
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import org.scalatest.Matchers | ||
import org.scalatest.prop.Checkers | ||
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/** ==The `arbitrary` Generator | ||
* | ||
* There is a special generator, `org.scalacheck.Arbitrary.arbitrary`, which generates arbitrary values of any | ||
* supported type. | ||
* | ||
* {{{ | ||
* val evenInteger = Arbitrary.arbitrary[Int] suchThat (_ % 2 == 0) | ||
* val squares = for { | ||
* xs <- Arbitrary.arbitrary[List[Int]] | ||
* } yield xs.map(x => x*x) | ||
* }}} | ||
* | ||
* The `arbitrary` generator is the generator used by ScalaCheck when it generates values for ''property'' parameters. | ||
* Most of the times, you have to supply the type of the value to `arbitrary`, like above, since Scala often can't | ||
* infer the type automatically. You can use `arbitrary` for any type that has an implicit `Arbitrary` instance. | ||
* As mentioned earlier, ScalaCheck has default support for common types, but it is also possible to define your own | ||
* implicit `Arbitrary` instances for unsupported types. See the following implicit Arbitrary definition for booleans, | ||
* that comes from the ScalaCheck implementation. | ||
* | ||
* {{{ | ||
* implicit lazy val arbBool: Arbitrary[Boolean] = Arbitrary(oneOf(true, false)) | ||
* }}} | ||
* | ||
* @param name arbitrary | ||
*/ | ||
object ArbitrarySection extends Checkers with Matchers with org.scalaexercises.definitions.Section { | ||
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import GeneratorsHelper._ | ||
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/** Let's see an example where we're defining an `implicit` `arbitrary` instance for `Char` | ||
*/ | ||
def implicitArbitraryChar(res0: Seq[Char]) = { | ||
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import org.scalacheck.Arbitrary | ||
import org.scalacheck.Gen | ||
import org.scalacheck.Prop.forAll | ||
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implicit lazy val myCharArbitrary = Arbitrary(Gen.oneOf('A', 'E', 'I', 'O', 'U')) | ||
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val validChars: Seq[Char] = res0 | ||
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check(forAll { c: Char => | ||
validChars.contains(c) | ||
}) | ||
} | ||
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/** This becomes more useful when we're dealing with our own data types. | ||
* We'll use the case class defined in the ''Generators Section'': | ||
* | ||
* {{{ | ||
* case class Foo(intValue: Int, charValue: Char) | ||
* }}} | ||
* | ||
* Having an implicit `def` or `val` of our data type in the scope allow us to use the `forAll` method without | ||
* specifying the ''generator'' | ||
*/ | ||
def implicitArbitraryCaseClass(res0: Boolean) = { | ||
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import org.scalacheck.Arbitrary | ||
import org.scalacheck.Gen | ||
import org.scalacheck.Prop.forAll | ||
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val fooGen = for { | ||
intValue <- Gen.posNum[Int] | ||
charValue <- Gen.alphaChar | ||
} yield Foo(intValue, charValue) | ||
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implicit lazy val myFooArbitrary = Arbitrary(fooGen) | ||
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check(forAll { foo: Foo => | ||
(foo.intValue < 0) == res0 && !foo.charValue.isDigit | ||
}) | ||
} | ||
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/** The `Arbitrary.arbitrary` method also returns a `Gen` object. | ||
*/ | ||
def useArbitraryOnGen(res0: Int) = { | ||
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import org.scalacheck.Arbitrary | ||
import org.scalacheck.Gen.listOfN | ||
import org.scalacheck.Prop.forAll | ||
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val genEightBytes = listOfN(8, Arbitrary.arbitrary[Byte]) | ||
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check(forAll(genEightBytes) { list => | ||
list.size == res0 | ||
}) | ||
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} | ||
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} |
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src/test/scala/exercises/scalachecklib/ArbitrarySpec.scala
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package exercises.scalachecklib | ||
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import org.scalacheck.Shapeless._ | ||
import org.scalatest.Spec | ||
import org.scalatest.prop.Checkers | ||
import shapeless.HNil | ||
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import scalachecklib.ArbitrarySection | ||
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class ArbitrarySpec extends Spec with Checkers { | ||
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def `implicit arbitrary char` = { | ||
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check( | ||
Test.testSuccess( | ||
ArbitrarySection.implicitArbitraryChar _, | ||
Seq('A', 'E', 'I', 'O', 'U') :: HNil | ||
) | ||
) | ||
} | ||
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def `implicit arbitrary case class` = { | ||
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check( | ||
Test.testSuccess( | ||
ArbitrarySection.implicitArbitraryCaseClass _, | ||
false :: HNil | ||
) | ||
) | ||
} | ||
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def `arbitrary on gen` = { | ||
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check( | ||
Test.testSuccess( | ||
ArbitrarySection.useArbitraryOnGen _, | ||
8 :: HNil | ||
) | ||
) | ||
} | ||
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} |