Mutators

Infection supports a set of Mutators which are based on AST and PHP-Parser project.

Read more about how to execute only particular set of mutators using Name column

Run the infection describe command to get information about mutators, right from the command line.

Function Signature

Name Original Mutated
PublicVisibility public function ... protected function ...
ProtectedVisibility protected function ... private function ...

To verify that the visibility of a method is necessary. If the visibility of a method can be reduced from public to protected or private, this may be an indication that the publicly accessible part of API of a class is larger than what’s strictly necessary. This mutator will drive the source code towards classes with smaller publicly accessible APIs and thus better encapsulation.

Unwrap Function

The Unwrap* mutator family will unwrap function parameters.

Name Original Mutated
UnwrapArrayChangeKeyCase $a = array_change_key_case(['foo' => 'bar']); $a = ['foo' => 'bar'];
UnwrapArrayChunk $a = array_chunk(['A', 'B', 'C'], 2); $a = ['A', 'B', 'C'];
UnwrapArrayColumn $a = array_column([['foo' => 'bar]], 'foo'); $a = [['foo' => 'bar]];
UnwrapArrayCombine $a = array_combine(['A', 'B', 'C'], ['foo', 'bar', 'baz']); $a = ['A', 'B', 'C'];
UnwrapArrayDiff $a = array_diff(['A', 'B', 'C'], ['D']); $a = ['A', 'B', 'C'];
UnwrapArrayDiffAssoc $a = array_diff_assoc(['foo' => 'bar'], ['baz' => 'bar]); $a = ['foo' => 'bar'];
UnwrapArrayDiffKey $a = array_diff_key(['foo' => 'bar'], ['baz' => 'bar]); $a = ['foo' => 'bar'];
UnwrapArrayDiffUassoc $a = array_diff_assoc(['foo' => 'bar'], ['baz' => 'bar], $keyCompareFunc); $a = ['foo' => 'bar'];
UnwrapArrayDiffUkey $a = array_diff_ukey(['foo' => 'bar'], ['baz' => 'bar], $keyCompareFunc); $a = ['foo' => 'bar'];
UnwrapArrayFilter $a = array_filter(['A', 1, 'C'], 'is_int'); $a = ['A', 1, 'C'];
UnwrapArrayFlip $a = array_flip(['A', 'B', 'C']); $a = ['A', 'B', 'C'];
UnwrapArrayIntersect $a = array_intersect(['A', 'B', 'C'], ['D']); $a = ['A', 'B', 'C'];
UnwrapArrayIntersectAssoc $a = array_intersect_assoc(['A', 'B', 'C'], ['D']); $a = ['A', 'B', 'C'];
UnwrapArrayIntersectKey $a = array_intersect_key(['foo' => 'bar'], ['bar' => 'baz']); $a = ['foo' => 'bar'];
UnwrapArrayIntersectUassoc $a = array_intersect_uassoc(['foo' => 'bar'], ['bar' => 'baz'], $keyCompareFunc); $a = ['foo' => 'bar'];
UnwrapArrayIntersectUkey $a = array_intersect_ukey(['foo' => 'bar'], ['bar' => 'baz'], $keyCompareFunc); $a = ['foo' => 'bar'];
UnwrapArrayKeys $a = array_keys(['foo' => 'bar']); $a = ['foo' => 'bar'];
UnwrapArrayMap $a = array_map('strtolower', ['A', 'B', 'C']); $a = ['A', 'B', 'C'];
UnwrapArrayMerge $a = array_merge(['A', 'B', 'C'], ['D']); $a = ['A', 'B', 'C'];
UnwrapArrayMergeRecursive $a = array_merge_recursive(['A', 'B', 'C'], ['D']); $a = ['A', 'B', 'C'];
UnwrapArrayPad $a = array_pad(['A'], 2, 'B'); $a = ['A'];
UnwrapArrayReduce $a = array_reduce(['A', 'B', 'C'], $callback, ['D']); $a = ['D'];
UnwrapArrayReplace $a = array_replace(['A', 'B', 'C'], ['D']); $a = ['A', 'B', 'C'];
UnwrapArrayReplaceRecursive $a = array_replace_recursive(['A', 'B', 'C'], ['D']); $a = ['A', 'B', 'C'];
UnwrapArrayReverse $a = array_reverse(['A', 'B', 'C']); $a = ['A', 'B', 'C'];
UnwrapArraySlice $a = array_slice(['A', 'B', 'C'], 1); $a = ['A', 'B', 'C'];
UnwrapArraySplice $a = array_splice(['A', 'B', 'C'], 1); $a = ['A', 'B', 'C'];
UnwrapArrayUdiff $a = array_udiff(['foo' => 'bar'], ['baz' => 'bar], $valueCompareFunc); $a = ['foo' => 'bar'];
UnwrapArrayUdiffAssoc $a = array_udiff_assoc(['foo' => 'bar'], ['baz' => 'bar], $valueCompareFunc); $a = ['foo' => 'bar'];
UnwrapArrayUdiffUassoc $a = array_udiff_uassoc(['foo' => 'bar'], ['baz' => 'bar], $valueCompareFunc, $keyCompareFunc); $a = ['foo' => 'bar'];
UnwrapArrayUintersect $a = array_uintersect(['foo' => 'bar'], ['baz' => 'bar], $valueCompareFunc); $a = ['foo' => 'bar'];
UnwrapArrayUintersectAssoc $a = array_uintersect_assoc(['foo' => 'bar'], ['baz' => 'bar], $valueCompareFunc); $a = ['foo' => 'bar'];
UnwrapArrayUintersectUassoc $a = array_uintersect_uassoc(['foo' => 'bar'], ['baz' => 'bar], $valueCompareFunc, $keyCompareFunc); $a = ['foo' => 'bar'];
UnwrapArrayUnique $a = array_unique(['foo', 'bar', 'bar']); $a = ['foo', 'bar', 'bar'];
UnwrapArrayValues $a = array_values(['foo' => 'bar']); $a = ['foo' => 'bar'];
UnwrapLcFirst $a = lcfirst('Hello, world!'); $a = 'Hello, world!';
UnwrapLtrim $a = ltrim(' Hello, world!'); $a = ' Hello, world!';
UnwrapRtrim $a = rtrim('Hello, world! '); $a = 'Hello, world! ';
UnwrapStrIreplace $a = str_ireplace('Afternoon', 'Evening' ,'Good Afternoon!'); $a = 'Good Afternoon!';
UnwrapStrRepeat $a = str_repeat('A', 3); $a = 'A';
UnwrapStrReplace $a = str_replace('Afternoon', 'Evening' ,'Good Afternoon!'); $a = 'Good Afternoon!';
UnwrapStrRev $a = strrev('Hello!'); `$a = ‘Hello!’;
UnwrapStrShuffle $a = str_shuffle('Hello!'); $a = 'Hello!';
UnwrapSubstr $a = substr('Hello!', 0, -1); $a = 'Hello!';
UnwrapStrToLower $a = strtolower('Hello!'); $a = 'Hello!';
UnwrapStrToUpper $a = strtoupper('Hello, world!'); $a = 'Hello, world!';
UnwrapTrim $a = trim(' Hello, world! '); $a = 'Hello, world!';
UnwrapUcFirst $a = ucfirst('hello, world!'); $a = 'hello, world!';
UnwrapUcWords $a = ucwords('hello, world!'); $a = 'hello, world!';

Binary Arithmetic

Name Original Mutated
Plus + -
Minus - +
Multiplication * /
Division / *
Modulus % *
Exponentiation ** /
MulEqual *= /=
PlusEqual += -=
MinusEqual -= +=
DivEqual /= *=
ModEqual %= *=
PowEqual **= /=
BitwiseAnd & |
BitwiseOr | &
BitwiseXor ^ &
BitwiseNot ~
ShiftRight >> <<
ShiftLeft << >>
AssignmentEqual == =
Assignment += =
Assignment -= =
Assignment *= =
Assignment **= =
Assignment /= =
Assignment %= =
Assignment .= =
Assignment &= =
Assignment |= =
Assignment ^= =
Assignment <<= =
Assignment >>= =
Assignment Coalesce ??= =

Round Family

The Round Family mutator will make sure that there’s enough tests to cover the rounding possibilities.

Name Original Mutated
RoundingFamily round() floor()
RoundingFamily round() ceil()
RoundingFamily ceil() floor()
RoundingFamily ceil() round()
RoundingFamily floor() round()
RoundingFamily floor() ceil()

Boolean

Name Original Mutated
ArrayItem [$a->foo => $b->bar] [$a->foo > $b->bar]
TrueValue true false
FalseValue false true
InstanceOf_ $a instanceof B true / false
LogicalAnd && ||
LogicalOr || &&
LogicalLowerAnd and or
LogicalLowerOr or and
LogicalNot !  
Yield_ yield $a => $b; yield $a > $b;
LogicalAndAllSubExprNegation $a = $b && $c; $a = !$b && !$c;
LogicalAndNegation $a = $b && $c; $a = !($b && $c);
LogicalAndSingleSubExprNegation $a = $b && $c; $a = !$b && $c;, $a = $b && !$c;
LogicalOrAllSubExprNegation $a = $b || $c; $a = !$b || !$c;
LogicalOrNegation $a = $b || $c; $a = !($b || $c);
LogicalOrSingleSubExprNegation $a = $b || $c; $a = !$b |&#124, $c; $a = $b || !$c;

TrueValue

Default settings:

infection.json5:

{
    "mutators": {
        "TrueValue": {
            "settings": {
                "in_array": true,
                "array_search": true
            }
        }
     }
}

Conditional Boundaries

Name Original Mutated
GreaterThan > >=
LessThan < <=
GreaterThanOrEqualTo >= >
LessThanOrEqualTo <= <

Equal or Identical Checks

Name Original Mutated
EqualIdentical == ===
NotEqualNotIdentical != !==
IdenticalEqual === ==
NotIdenticalNotEqual !== !=

These mutators are disabled by default, you can use the @equal or @identical profiles to enable the ones you prefer.

Negated Conditionals

Name Original Mutated
Equal == !=
NotEqual != ==
Identical === !==
NotIdentical !== ===
GreaterThanNegotiation > <=
LessThanNegotiation < >=
GreaterThanOrEqualToNegotiation >= <
LessThanOrEqualToNegotiation <= >

Operator

Name Original Mutated
Catch_ catch (\Throwable&#124;\DomainException $e) catch (\DomainException $e) catch (\DomainException $e)
Coalesce $foo ?? $bar $bar ?? $foo
Concat $foo . $bar $bar . $foo
NullSafeMethodCall $object?->getObject() $object->getObject()
NullSafePropertyCall $object?->property $object->property
SpreadAssignment $array = [...$collection] $array = $collection
SpreadOneItem [...$collection, 2, 3] [[...$collection][0], 2, 3]
SpreadRemoval [...$collection, 2, 3] [$collection, 2, 3]
Ternary isset($b) ? 'B' : 'C' isset($b) ? 'C' : 'B'
ElseIfNegation } elseif ($this->bar()) { } elseif (!$this->bar()) {
IfNegation if ($this->fooBar()) { if (!$this->fooBar()) {

Increments

Name Original Mutated
Increment ++ --
Decrement -- ++

Return Values

Name Original Mutated
ArrayOneItem return $collection; return count($collection) > 1 ? array_slice($collection, 0, 1, true) : $collection;
TrueValue return true; return false;
FalseValue return false; return true;
IntegerNegation return (Any Integer); return -(Any Integer);
OneZeroFloat return 0.0; return 1.0;
OneZeroFloat return 1.0; return 0.0;
FloatNegation return (Any Float); return -(Any Float);
This return $this; return null;
FunctionCall return function(); function(); return null;
NewObject return new Class(); new Class(); return null;
YieldValue yield $key => $value; yield $value;

Removal Mutators

Name Original Mutated
ArrayItemRemoval [1, $a, '3'] [$a, '3'] depending on configuration
FunctionCallRemoval foo_bar($a) -
MethodCallRemoval $this->method($var) -
CatchBlockRemoval try {} catch (\DomainException $e) {} catch (\Throwable $e) {} try {} catch (\DomainException $e) {} try {} catch (\Throwable $e) {}
MatchArmRemoval match ($x) { 1 => null, default => throw new \Exception()}; match ($x) { default => throw new \Exception()}; match ($x) { 1 => null};
CloneRemoval clone (new stdClass()) new stdClass()
ConcatOperandRemoval 'foo' . 'bar' 'bar' and 'foo'
SharedCaseRemoval switch($a) { case 'a': case 'b': break; } switch($a) { case 'b': break; } switch($a) { case 'a': break; }

ArrayItemRemoval

Configuration options:

When using all option we advise to set the limit as well

You should remember to exclude files containing large arrays (like configuration)
when using ArrayItemRemoval mutator in all mode

infection.json5:

{
    "mutators": {
        "ArrayItemRemoval": {
            "settings": {
                "remove": "all",
                "limit": 15
            }
        }
     }
}

Loop

Name Original Mutated
Break_ break; continue;
Continue_ continue; break;
Foreach_ foreach ($someVar as …); foreach ([] as …);
For_ for ($i=0; $i < 10; $i++); for ($i=0; false; $i++);
While_ while ($condition); while (false);
DoWhile do {} while ($condition); do {} while (false);

Sorting

Name Original Mutated
Spaceship $a <=> $b $b <=> $a

Literal Numbers

Name Original Mutated
OneZeroFloat 0.0 1.0
OneZeroFloat 1.0 0.0
DecrementInteger 7 6
IncrementInteger 7 8

Exceptions

Name Original Mutated
Throw_ throw new NotFoundException(); new NotFoundException();
Finally_ try {} catch (\Exception $e) {} finally {} try {} catch (\Exception $e) {}
UnwrapFinally try { $callback(); } finally { $cleanUpCallbak(); } $callback(); $cleanUpCallbak();

Type Casting

Name Original Mutated
CastArray (array) $value; $value
CastBool (bool) $value; $value
CastFloat (float) $value; $value
CastInt (int) $value; $value
CastObject (object) $value; $value
CastString (string) $value; $value

Regex

Name Original Mutated
PregQuote $a = preg_quote('text'); $a = 'text';
PregMatchMatches preg_match('/pattern/', $value, $matches); (int) $matches = array();
PregMatchRemoveCaret preg_match('/^test/', $string); preg_match('/test/', $string);
PregMatchRemoveDollar preg_match('/test$/', $string); preg_match('/test/', $string);
PregMatchRemoveFlags preg_match('/test$/iu', $string); preg_match('/test$/u', $string);, preg_match('/test$/i', $string);

Extensions

BCMath

Name Original Mutated
BCMath bcadd($a, $b, $mod); (string) ($a + $b);
bcdiv($a, $b, $mod); (string) ($a / $b);
bcmod($a, $b, $mod); (string) ($a % $b);
bcmul($a, $b, $mod); (string) ($a * $b);
bcpow($a, $b, $mod); (string) ($a ** $b);
bcsub($a, $b, $mod); (string) ($a - $b);
bcsqrt($a, $mod); (string) \sqrt($a);
bcpowmod($a, $b, $c, $mod); (string) (\pow($a, $b) % $c);
bccomp($a, $b, $mod); $a <=> $b;

infection.json5:

{
    "mutators": {
        "BCMath": {
            "settings": {
                "bcpowmod": false,
                "bccomp": false
            }
        }
     }
}

MBString

Name Original Mutated
MBString mb_chr($code); chr($code);
mb_ord($character); ord($character);
mb_parse_str('text', $results); parse_str('text', $results);
mb_send_mail($to, $subject, $message, $headers, $parameters); mail($to, $subject, $message, $headers, $parameters);
mb_strcut('text', 0, 123, 'utf-8'); substr('text', 0, 123);
mb_stripos('text', 't', 0, 'utf-8'); stripos('text', 't', 0);
mb_stristr('text', 't', true, 'utf-8'); stristr('text', 't', true);
mb_strlen('text', 'utf-8'); strlen('text');
mb_strpos('text', 't', 0, 'utf-8'); strpos('text', 't', 0);
mb_strrchr('text', 't', true, 'utf-8'); strrchr('text', 't', true);
mb_strripos('text', 't', 0, 'utf-8'); strripos('text', 't', 0);
mb_strrpos('text', 't', 0, 'utf-8'); strrpos('text', 't', 0);
mb_strstr('text', 't', true, 'utf-8'); strstr('text', 't', true);
mb_strtolower('text', 'utf-8'); strtolower('text');
mb_strtoupper('text', 'utf-8'); strtoupper('text');
mb_substr_count('text', 't', 'utf-8'); substr_count('text', 't');
mb_substr('text', 0, 123, 'utf-8'); substr('text', 0, 123);
mb_str_split('text', 2, 'utf-8'); str_split('text', 2);
mb_convert_case('text', $mode); strtoupper('text');, strtolower('text'); or ucwords('text'); depending on mode

Some of the functions are not supported due to complexity to convert them to standard string manipulation functions.
Implementing them either does not make sense or creates too many false positive mutations.
Not supported functions are mb_ereg*, mb_split, mb_strrichr, mb_get_info and similar.

infection.json5:

{
    "mutators": {
        "MBString": {
            "settings": {
                "mb_send_mail": false,
                "mb_substr_count": false
            }
        }
     }
}
Caught a mistake or want to contribute to the documentation? Edit this page on Github!