Weapon regeX

Weapon regeX mutates regular expressions for use in mutation testing. It has been designed from the ground up to support Stryker Mutator. Weapon regeX is available for both JavaScript and Scala and is used in Stryker4s and StrykerJS flavors of Stryker. The JavaScript version of the library is generated from Scala using Scala.js. The generated mutant regular expressions cover human errors, such as edge cases and typos. A list of provided mutators is given below. For an introduction to mutation testing, see Stryker's website.

The current supported versions for Scala are: 2.12, 2.13 and 3.

Getting started

In case you want to incorporate Weapon-regeX into your project.

Scala

Add Weapon regeX to your build.sbt :

libraryDependencies += "io.stryker-mutator" %% "weapon-regex" % weaponRegexVersion

Mutate!

import weaponregex.WeaponRegeX

WeaponRegeX.mutate("^abc(d+|[xyz])$") match {
    case Right(mutants) => mutants map (_.pattern)
    case Left(e)        => throw new RuntimeException(e)
}
// res0: Seq[String] = List(
//   "abc(d+|[xyz])$",
//   "^abc(d+|[xyz])",
//   "\\Aabc(d+|[xyz])$",
//   "^abc(?:d+|[xyz])$",
//   "^abc(d|[xyz])$",
//   "^abc(d{0,}|[xyz])$",
//   "^abc(d{2,}|[xyz])$",
//   "^abc(d{1}|[xyz])$",
//   "^abc(d+?|[xyz])$",
//   "^abc(d+|[^xyz])$",
//   "^abc(d+|[yz])$",
//   "^abc(d+|[xz])$",
//   "^abc(d+|[xy])$",
//   "^abc(d+|[\\w\\W])$",
//   "^abc(d+|[xyz])\\z"
// )

JavaScript

Install Weapon regeX with npm.

npm install weapon-regex

Mutate!

import wrx from 'weapon-regex';

let mutants = wrx.mutate('^abc(d+|[xyz])$');

mutants.forEach((mutant) => {
    console.log(mutant.pattern);
});

Note: as of 1.0.0 weapon-regex uses ES Modules.

API

Scala

The mutate function has the following signature:

import weaponregex.model.mutation._
import weaponregex.mutator.BuiltinMutators
import weaponregex.parser.{ParserFlavor, ParserFlavorJVM}

def mutate(
              pattern       : String,
              mutators      : Seq[TokenMutator] = BuiltinMutators.all,
              mutationLevels: Seq[Int] = null,
              flavor        : ParserFlavor = ParserFlavorJVM
          ): Either[String, Seq[Mutant]] = ???

With the mutators argument you can give a select list of mutators that should be used in the mutation process. If omitted, all built-in mutators will be used. This list will be filtered depending on the mutationLevels argument.

A list of mutationLevels can also be passed to the function. The mutators will be filtered based on the levels in the list. If omitted, no filtering takes place.

The flavor argument allows setting the parser flavor that will be used to parse the pattern. Currently, we support a ParserFlavorJVM and ParserFlavorJS. By default in Scala the JVM flavor is used.

This function will return a Right with Seq[Mutant] if it can be parsed, or a Left with the error message otherwise.

JavaScript

The mutate function can be called with regular expression flags and an options object to control which mutators and which parser flavor should be used in the mutation process:

import wrx from 'weapon-regex';

let mutants = wrx.mutate('^abc(d+|[xyz])$', 'u', {
    mutators: Array.from(wrx.mutators.values()),
    mutationLevels: [1, 2, 3],
    flavor: wrx.ParserFlavorJS,
});

Both options can be omitted, and have the same functionality as the options described in the Scala API section. By default in JS the JS parser flavor is used. You can get a map of mutators from the mutators attribute of the library. It is a Map from string (mutator name) to a mutator object.

This function will return a JavaScript Array of Mutant if it can be parsed, or throw an exception otherwise.

Supported mutators

All the supported mutators and at which mutation level they appear are shown in the table below.

Name	1	2	3
BOLRemoval	✅	✅	✅
EOLRemoval	✅	✅	✅
BOL2BOI		✅	✅
EOL2EOI		✅	✅
CharClassNegation	✅
CharClassChildRemoval		✅	✅
CharClassAnyChar		✅	✅
CharClassRangeModification			✅
PredefCharClassNegation	✅
PredefCharClassNullification		✅	✅
PredefCharClassAnyChar		✅	✅
UnicodeCharClassNegation	✅
QuantifierRemoval	✅
QuantifierNChange		✅	✅
QuantifierNOrMoreModification		✅	✅
QuantifierNOrMoreChange		✅	✅
QuantifierNMModification		✅	✅
QuantifierShortModification		✅	✅
QuantifierShortChange		✅	✅
QuantifierReluctantAddition			✅
GroupToNCGroup		✅	✅
LookaroundNegation	✅	✅	✅

Boundary Mutators

BOLRemoval

Remove the beginning of line character ^.

Original	Mutated
^abc	abc

Back to table 🔝

EOLRemoval

Remove the end of line character $.

Original	Mutated
abc$	abc

Back to table 🔝

BOL2BOI

Change the beginning of line character ^ to a beginning of input character \A.

Original	Mutated
^abc	\Aabc

Back to table 🔝

EOL2EOI

Change the end of line character ^ to a end of input character \z.

Original	Mutated
abc$	abc\z

Back to table 🔝

Character class mutators

CharClassNegation

Flips the sign of a character class.

Original	Mutated
[abc]	[^abc]
[^abc]	[abc]

Back to table 🔝

CharClassChildRemoval

Remove a child of a character class.

Original	Mutated
[abc]	[bc]
[abc]	[ac]
[abc]	[ab]

Back to table 🔝

CharClassAnyChar

Change a character class to a character class which matches any character.

Original	Mutated
[abc]	[\w\W]

Back to table 🔝

CharClassRangeModification

Change the high and low of a range by one in both directions if possible.

Original	Mutated
[b-y]	[a-y]
[b-y]	[c-y]
[b-y]	[b-z]
[b-y]	[b-x]

Back to table 🔝

Predefined character class mutators

PredefCharClassNegation

Flips the sign of a predefined character class. All the predefined character classes are shown in the table below.

Original	Mutated
\d	\D
\D	\d
\s	\S
\S	\s
\w	\W
\W	\w

Back to table 🔝

PredefCharClassNullification

Remove the backslash from a predefined character class such as \w.

Original	Mutated
\d	d
\D	D
\s	s
\S	S
\w	w
\W	W

Back to table 🔝

PredefCharClassAnyChar

Change a predefined character class to a character class containing the predefined one and its negation.

Original	Mutated
\d	[\d\D]
\D	[\D\d]
\s	[\s\S]
\S	[\S\s]
\w	[\w\W]
\W	[\W\w]

Back to table 🔝

UnicodeCharClassNegation

Flips the sign of a Unicode character class.

Original	Mutated
\p{Alpha}	\P{Alpha}
\P{Alpha}	\p{Alpha}

Back to table 🔝

Quantifier mutators

QuantifierRemoval

Remove a quantifier. This is done for all possible quantifiers, even ranges, and the reluctant and possessive variants.

Original	Mutated
abc?	abc
abc*	abc
abc+	abc
abc{1,3}	abc
abc??	abc
abc*?	abc
abc+?	abc
abc{1,3}?	abc
abc?+	abc
abc*+	abc
abc++	abc
abc{1,3}+	abc

Back to table 🔝

QuantifierNChange

Change the fixed amount quantifier to a couple of range variants.

Original	Mutated
abc{9}	abc{0,9}
abc{9}	abc{9,}

Back to table 🔝

QuantifierNOrMoreModification

Change the n to infinity range quantifier to a couple of variants where the low of the range is incremented and decremented by one.

Original	Mutated
abc{9,}	abc{8,}
abc{9,}	abc{10,}

Back to table 🔝

QuantifierNOrMoreChange

Turn an n or more range quantifier into a fixed number quantifier.

Original	Mutated
abc{9,}	abc{9}

Back to table 🔝

QuantifierNMModification

Alter the n to m range quantifier by decrementing or incrementing the high and low of the range by one.

Original	Mutated
abc{3,9}	abc{2,9}
abc{3,9}	abc{4,9}
abc{3,9}	abc{3,8}
abc{3,9}	abc{3,10}

Back to table 🔝

QuantifierShortModification

Treat the shorthand quantifiers (?, *, +) as their corresponding range quantifier variant ({0,1}, {0,}, {1,}), and applies the same mutations as mentioned in the mutators above.

Original	Mutated
abc?	abc{1,1}
abc?	abc{0,0}
abc?	abc{0,2}
abc*	abc{1,}
abc+	abc{0,}
abc+	abc{2,}

Back to table 🔝

QuantifierShortChange

Change the shorthand quantifiers * and + to their fixed range quantifier variant.

Original	Mutated
abc*	abc{0}
abc+	abc{1}

Back to table 🔝

QuantifierReluctantAddition

Change greedy quantifiers to reluctant quantifiers.

Original	Mutated
abc?	abc??
abc*	abc*?
abc+	abc+?
abc{9}	abc{9}?
abc{9,}	abc{9,}?
abc{9,13}	abc{9,13}?

Back to table 🔝

Group-related construct mutators

GroupToNCGroup

Change a normal group to a non-capturing group.

Original	Mutated
(abc)	(?:abc)

Back to table 🔝

LookaroundNegation

Flips the sign of a lookaround (lookahead, lookbehind) construct.

Original	Mutated
(?=abc)	(?!abc)
(?!abc)	(?=abc)
(?<=abc)	`(?