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Supported mutators

All Stryker versions support a variety of different mutators. The difference in support is listed below.

Support

Mutator Stryker Stryker.NET Stryker4s
Arithmetic Operator
Array Declaration
Assignment Expression n/a
Block Statement
Boolean Literal
Checked Statement n/a n/a
Conditional Expression
Equality Operator
Logical Operator
Method Expression
String Literal
Unary Operator
Update Operator n/a

Arithmetic Operator

Original Mutated
a + b a - b
a - b a + b
a * b a / b
a / b a * b
a % b a * b

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Array Declaration

Original Mutated
new Array(1, 2, 3, 4) new Array()
[1, 2, 3, 4] [ ]

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Assignment Expression

Original Mutated
+= -=
-= +=
*= /=
/= *=
%= *=
<<= >>=
>>= <<=
&= |=
|= &=

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Block Statement

Removes the content of every block statement. For example the code:

function saySomething() {
  console.log('Hello world!');
}

becomes:

function saySomething() {
}

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Boolean Literal

Original Mutated
true false
false true
!(a == b) a == b ¹
  • ¹: Not supported by Stryker4s

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Checked Statement

Stryker.NET specific mutator

Original Mutated
checked(2 + 4) 2 + 4

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Conditional Expression

Original Mutated
for (var i = 0; i < 10; i++) { } for (var i = 0; false; i++) { } ¹
while (a > b) { } while (false) { }
do { } while (a > b); do { } while (false);
if (a > b) { } if (true) { }
if (a > b) { } if (false) { }
var x = a > b ? 1 : 2; var x = true ? 1 : 2; ¹
var x = a > b ? 1 : 2; var x = false ? 1 : 2; ¹
  • ¹: Not supported by Stryker4s

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Equality Operator

Original Mutated
a < b a <= b
a < b a >= b
a <= b a < b
a <= b a > b
a > b a >= b
a > b a <= b
a >= b a > b
a >= b a < b
a == b a != b
a != b a == b
a === b a !== b ¹
a !== b a === b ¹
  • ¹: Only supported on StrykerJS and Stryker4s

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Logical Operator

Original Mutated
a && b a || b
a || b a && b

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Method Expression

Due to differences in language syntax, method expressions are implemented differently in each Stryker framework:

Stryker.NET:

Original Mutated
Distinct()
Reverse()
OrderBy()
OrderByDescending()
SingleOrDefault() FirstOrDefault()
FirstOrDefault() SingleOrDefault()
First() Last()
Last() First()
All() Any()
Any() All()
Skip() Take()
Take() Skip()
SkipWhile() TakeWhile()
TakeWhile() SkipWhile()
Min() Max()
Max() Min()
Sum() Count()
Count() Sum()

Stryker4s:

Original Mutated
a.filter(b) a.filterNot(b)
a.filterNot(b) a.filter(b)
a.exists(b) a.forall(b)
a.forall(b) a.exists(b)
a.take(b) a.drop(b)
a.drop(b) a.take(b)
a.takeRight(b) a.dropRight(b)
a.dropRight(b) a.takeRight(b)
a.takeWhile(b) a.dropWhile(b)
a.dropWhile(b) a.takeWhile(b)
a.isEmpty a.nonEmpty
a.nonEmpty a.isEmpty
a.indexOf a.lastIndexOf(b)
a.lastIndexOf(b) a.indexOf(b)
a.max a.min
a.min a.max
a.maxBy(b) a.minBy(b)
a.minBy(b) a.maxBy(b)

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String Literal

Original Mutated
"foo" (non-empty string) "" (empty string)
"" (empty string) "Stryker was here!"
s"foo ${bar}" (string interpolation) s"" ¹

¹ For Stryker4s, only works with string interpolation and not other types of interpolation (like Scalameta quasiquotes) to avoid compile errors

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Unary Operator

Original Mutated
+a -a
-a +a

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Update Operator

Original Mutated
a++ a--
a-- a++
++a --a
--a ++a

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