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 :

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

Mutate!

`scala
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.

`bash
npm install weapon-regex
`

Mutate!

`javascript
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.

![Try it!](https://npm.runkit.com/weapon-regex)

API

Scala

The mutate function has the following signature:

`scala
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:

`js
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

$3

Remove the beginning of line character ^.

| Original | Mutated |
|----------|---------|
| ^abc | abc |

Back to table 🔝

$3

Remove the end of line character $.

| Original | Mutated |
|----------|---------|
| abc$ | abc |

Back to table 🔝

$3

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

| Original | Mutated |
|----------|---------|
| ^abc | \Aabc |

Back to table 🔝

$3

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

| Original | Mutated |
|----------|---------|
| abc$ | abc\z |

Back to table 🔝

Character class mutators

$3

Flips the sign of a character class.

| Original | Mutated |
|----------|----------|
| [abc] | [^abc] |
| [^abc] | [abc] |

Back to table 🔝

$3

Remove a child of a character class.

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

Back to table 🔝

$3

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

| Original | Mutated |
|----------|----------|
| [abc] | [\w\W] |

Back to table 🔝

$3

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

$3

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 🔝

$3

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 🔝

$3

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 🔝

$3

Flips the sign of a Unicode character class.

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

Back to table 🔝

Quantifier mutators

$3

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 🔝

$3

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 🔝

$3

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 🔝

$3

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

| Original | Mutated |
|-----------|----------|
| abc{9,} | abc{9} |

Back to table 🔝

$3

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 🔝

$3

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 🔝

$3

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

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

Back to table 🔝

$3

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

$3

Change a normal group to a non-capturing group.

| Original | Mutated |
|----------|-----------|
| (abc) | (?:abc) |

Back to table 🔝

$3

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

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

Back to table 🔝