Scalactic

<!DOCTYPE html> <html> <head> <meta http-equiv="content-type" content="text/html;charset=utf-8" /> <title>Scalactic</title> <link rel="Stylesheet" href="/assets/stylesheets/main.css" type="text/css" media="screen"/>  <script async src="https://www.googletagmanager.com/gtag/js?id=G-19BZD1XMRV"></script> <script defer src='/assets/javascripts/gtag.js'></script> </head> <body> <div class="Container">  <script id="adsArtimaScript" type="text/javascript" src="https://www.artima.com/assets/javascripts/4ca150665e51d0b1c3890ca1b891c507-ads.js?product=Scalactic"></script> <div id="Header"> <div id="Nav"> Home | <a href="/quick_start">Quick Start</a> | <a href="/install">Install</a> | <a href="/user_guide">User Guide</a> | <a href="/scaladoc">Scaladoc</a> | <a href="/supersafe">SuperSafe</a> | <a href="/about">About</a> </div>  </div>  <div id="body"> <div class="homePageMessage"> <img src="/assets/images/scalacticHeading.gif" width="700" height="200" alt="Scalactic: Simply Productive"/> </div> Latest Release - <a href="http://www.scalatest.org/release_notes/3.2.19">Scalactic 3.2.19</a>! <div style="text-align: left"> The Scalactic library is focused on constructs related to quality that are useful in both production code and tests. Although <a href="http://scalatest.org">ScalaTest</a> is tightly integrated with Scalactic, you can use Scalactic with any Scala project and any test framework. The Scalactic library has no dependencies other than Scala itself. <h1>The <code>===</code> and <code>!==</code> operators</h1> Scalactic provides a powerful <code>===</code> operator (and its complement, <code>!==</code>) that allows you to <ul> <li>Customize equality for a type outside its class</li> <li>Get compiler errors for suspicious equality comparisons</li> <li>Compare numeric values for equality with a tolerance</li> <li>Normalize values before comparing them for equality</li> </ul> For example, you can compare strings for equality after being normalized by forcing them to lowercase by customizing <a href='/scaladoc/3.2.19/org/scalactic/Equality.html'><code>Equality</code></a> explicitly, like this: <pre class="scala"> import org.scalactic._ import TripleEquals._ import StringNormalizations._ import Explicitly._ ("Hello" === "hello") (after being lowerCased) // true </pre> You can also define implicit <a href='/scaladoc/3.2.19/org/scalactic/Normalization.html'><code>Normalization</code></a> strategies for types and access them by invoking <code>norm</code> methods: <pre class="scala"> import NormMethods._ implicit val strNormalization = lowerCased "WHISPER".norm // "whisper" "WHISPER".norm === "whisper" // true </pre> The “<code>after being lowerCased</code>” syntax shown previously is provided by Scalactic' <a href='/scaladoc/3.2.19/org/scalactic/Explicitly.html'><code>Explicitly</code></a> DSL, which allows you to specify <code>Equality</code> explicitly. You can also define custom <code>Equality</code>s implicitly: <pre class="scala"> implicit val strEquality = decided by defaultEquality[String] afterBeing lowerCased "Hello" === "hello" // true "normalized" === "NORMALIZED" // true </pre> You can compare numeric values for equality with a <a href='/scaladoc/3.2.19/org/scalactic/Tolerance.html'><code>Tolerance</code></a>, like this: <pre class="scala"> import Tolerance._ 2.00001 === 2.0 +- 0.01 // true </pre> Or you could use <a href='/scaladoc/3.2.19/org/scalactic/TolerantNumerics.html'><code>TolerantNumerics</code></a> define an implicit <code>Equality[Double]</code> that compares <code>Double</code>s with a tolerance: <pre class="scala"> import TolerantNumerics._ implicit val dblEquality = tolerantDoubleEquality(0.01) 2.00001 === 2.0 // true </pre> A compiler error for an equality comparison that would always yield false looks like: <pre class="scala"> import TypeCheckedTripleEquals._ Some("hi") === "hi" error: types Some[String] and String do not adhere to the type constraint selected for the === and !== operators; the missing implicit parameter is of type org.scalactic.Constraint[Some[String],String] Some("hi") === "hi" ^ </pre> <h1><code>Or</code> and <code>Every</code></h1> Scalactic provides an “<code>Either</code> with attitude” named <a href='/scaladoc/3.2.19/org/scalactic/Or.html'><code>Or</code></a>, designed for functional error handling. <code>Or</code> gives you more convenient chaining of <code>map</code> and <code>flatMap</code> calls (and <code>for</code> expressions) than <code>Either</code> and, when, combined with <a href='/scaladoc/3.2.19/org/scalactic/Every.html'><code>Every</code></a>, enables you to accumulate errors. <code>Every</code> is an ordered collection of one or more elements. An <code>Or</code> is either <a href='/scaladoc/3.2.19/org/scalactic/Good.html'><code>Good</code></a> or <a href='/scaladoc/3.2.19/org/scalactic/Bad.html'><code>Bad</code></a>. An <code>Every</code> is either <a href='/scaladoc/3.2.19/org/scalactic/One.html'<code>One</code></a> or <a href='/scaladoc/3.2.19/org/scalactic/Many.html'><code>Many</code></a>. Here's an example of accumulating errors with <code>Or</code> and <code>Every</code>: <pre class="scala"> import org.scalactic._ import Accumulation._ case class Person(name: String, age: Int) def parseName(input: String): String Or One[ErrorMessage] = { val trimmed = input.trim if (!trimmed.isEmpty) Good(trimmed) else Bad(One(s""""${input}" is not a valid name""")) } def parseAge(input: String): Int Or One[ErrorMessage] = { try { val age = input.trim.toInt if (age >= 0) Good(age) else Bad(One(s""""${age}" is not a valid age""")) } catch { case _: NumberFormatException => Bad(One(s""""${input}" is not a valid integer""")) } } def parsePerson(inputName: String, inputAge: String): Person Or Every[ErrorMessage] = { val name = parseName(inputName) val age = parseAge(inputAge) withGood(name, age) { Person(_, _) } } </pre> Here are some examples of <code>parsePerson</code> in action: <pre class="scala"> parsePerson("Bridget Jones", "29") // Result: Good(Person(Bridget Jones,29)) parsePerson("Bridget Jones", "") // Result: Bad(One("" is not a valid integer)) parsePerson("Bridget Jones", "-29") // Result: Bad(One("-29" is not a valid age)) parsePerson("", "") // Result: Bad(Many("" is not a valid name, "" is not a valid integer)) </pre> <code>Or</code> offers several other ways to accumulate errors besides the <code>withGood</code> methods shown in the example above. See the <a href='/scaladoc/3.2.19/org/scalactic/Or.html'>documentation for <code>Or</code></a> for more information. <h1><code>Requirements</code> and <code>Snapshots</code></h1> Scalactic includes a <a href='/scaladoc/3.2.19/org/scalactic/Requirements.html'><code>Requirements</code></a> trait that offers <code>require</code>, <code>requireState</code>, and <code>requireNonNull</code> methods for checking pre-conditions that give descriptive error messages extracted via a macro. Here are some examples: <pre class="scala"> val a = -1 require(a >= 0) // throws IllegalArgumentException: -1 was not greater than or equal to 0 requireState(a >= 0) // throws IllegalStateException: -1 was not greater than or equal to 0 val b: String = null requireNonNull(a, b) // throws NullPointerException: b was null </pre> Trait <a href='/scaladoc/3.2.19/org/scalactic/Snapshots.html'><code>Snapshots</code></a> offers a <code>snap</code> method that can help you make debug and log messages that include information about the values of variables: <pre class="scala"> val a = 1 val b = '2' val c = "3" snap(a, b, c) // Result: a was 1, b was '2', c was "3" </pre> <h1>And more (but not much more)...</h1> Scalactic also includes a <a href='/scaladoc/3.2.19/org/scalactic/TimesOnInt.html'><code>TimesOnInt</code></a> trait that allows you to perform side-effecting loops a specified number of times, like this: <pre class="scala"> import TimesOnInt._ 3 times println("hello ") // Output: hello hello hello </pre> You can also define an alternate <code>String</code> forms for types using <a href='/scaladoc/3.2.19/org/scalactic/Prettifier.html'><code>Prettifier</code></a>s and create extractors for <code>Throwable</code>s via the <a href='/scaladoc/3.2.19/org/scalactic/Catcher.html'><code>Catcher</code></a> factory. And that's it: Scalactic is a small, very focused library. Why not give it a try? Just visit the <a href="/quick_start">Quick Start</a> page. </div>  <div style="font-size: 66%; margin-top: 60px"> Scalactic is brought to you by Bill Venners, with contributions from several other folks. It is sponsored by Artima, Inc. ScalaTest is free, open-source software released under the <a href="http://www.apache.org/licenses/LICENSE-2.0.html">Apache 2.0 license</a>. Copyright © 2009-2025 Artima, Inc. All Rights Reserved. <a href="http://www.artima.com" class="no_link_hover"> <img src="/assets/images/artima100Black.png" style="margin-top: 2px" width="100" height="38" alt="artima"/> </a> </div>  </div>  </body> </html>

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Scalactic