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Type Sensitive Application of Mutation Operators for Dynamically Typed Programs

Type Sensitive Application of Mutation Operators for Dynamically Typed Programs. Leonardo Bottaci Department of Computer Science University of Hull, Hull, UK. Mutation of Strongly typed Programs. Variables and operators in expressions are typed.

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Type Sensitive Application of Mutation Operators for Dynamically Typed Programs

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  1. Type Sensitive Application of Mutation Operators for Dynamically Typed Programs Leonardo BottaciDepartment of Computer ScienceUniversity of Hull, Hull, UK

  2. Mutation of Strongly typed Programs • Variables and operators in expressions are typed. • Mutation operators can be applied in a type sensitive manner. original program mutant program String s; String s inti, j; inti, j; … … i abs(i), … j

  3. Mutation of Weakly Typed Programs Variables and operators in expressions are not typed. How can mutation operators can be applied in a type sensitive manner? original program mutant program vars; vars vari, j; vari, j; … … iabs(i), abs(s) … j… s 3

  4. Basic Idea • Generate mutants dynamically. • Represent mutants of the original program using a meta-mutant, (mutant schemata, parameterised mutant.) orig program meta-mutant x = y + z; assign(m(x), arith(m(y), m(z))) m(x) mutates variable x, e.g. abs(x) , y arith(y, z) mutates arithmetic operator, e.g. z - y assign(x, e) mutates assign operator, e.g. x += e, x -= e

  5. Meta-mutant for Strongly Typed Program m(x) { switch(mutantOfx) { none: return x; abs: return abs(x); inc: return x + 1; y: return y; … }} x is known to be of type int, say, this allows cases to be determined at meta-mutant generation time. 5

  6. Meta-mutant for Weakly Typed Program m(x) { if (none) { return x; } else { determine, from the value of x, the appropriate mutants update mutants in mutant table for x set nextMutant in table return mutantTable[nextMutant] }} 6

  7. Object Value Mutations In JavaScript, members of object are dynamic. x = {student: {name: "John", number: "0232"}, grade: 45}; x.student.name = "Jane"; Mutate the terminal or leaf properties only. Property deletion, property value mutation. Again, discover these properties at mutant execution time. 7

  8. Variable Replacement Mutations To replace variable x with variable y, they should hold values of compatible type. m(x) can determine the type of x only. Hence perform mutation in two phases Value mutation phase, e.g. return abs(x) Record types of all variables in this phase Replacement mutation phase, e.g. return y Use types recorded in value mutation phase 8

  9. Summary • Weakly typed languages are popular, especially for web programming, (e.g. JavaScript). • In such languages, type errors are not caught by the compiler and so additional testing is required. • Investigate advantages and disadvantages of mutation testing for weakly typed languages. • A prototype tool has been developed for mutating JavaScript programs.

  10. Issues JavaScript programs make use large objects created outside of the program, e.g. browser document objects, - to what extent should these be mutated? The JavaScript execution environments, language implementations, vary – good source for mutations. How weakly typed are programs in practice? 10

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