Sharing Mutation in Java

Package Installed

• junit official site
• org.pitest official site

How To Run

• mvn compile
• mvn test
• mvn org.pitest:pitest-maven:mutationCoverage

Mutation Report

You will find report at {project dir}\target\pit-reports

What's mutation test

Wiki

Mutation test is a way to test your unit test and production code is good enough or not.

Mutators PIT provide

examples and description below can find in ref link.

ref

Default group

• Conditionals Boundary Mutator

mutate operators <, <=, >, >=

ex:

 if (a > b) {
  System.out.println("a is bigger than b");
}

will be mutate to

if (a >= b) {
  System.out.println("a is bigger than b");
}

• Increments Mutor

only mutate local veriables

public int Increment(int i) {
  i++;
  return i;
}

will be mutate to

public int Increment(int i) {
  i--;
  return i;
}

• Invert Negatives Mutor

inverts negation of integer and floating point numbers

public float negate(final float i) {
  return -i;
}

will be mutate to

public float negate(final float i) {
  return i;
}

• Math Mutor

replaces binary arithmetic operations for either integer or floating-point arithmetic with another operation

double num3 = num1 + num2;

will be mutate to

double num3 = num1 - num2;

• Negate Conditionals Mutor

mutate conditionals

if (a == b) {
  System.out.println("a is equal to b");
}

will be mutate to

if (a != b) {
  System.out.println("a is equal to b");
}

• Return Values Mutator

mutates the return values of method calls

different from return type, if value type then change to default or opposite value, if reference type then return null, if return null then throw java.lang.RuntimeException

public Object foo() {
  return new Object();
}

will be mutate to

public Object foo() {
  new Object();
  return null;
}

• Void Method Calls

removes method calls to void methods

public void someVoidMethod(int i) {
  System.out.println("call method someVoidMethod");
}

public int foo() {
  int i = 5;
  someVoidMethod(i);
  return i;
}

will be mutate to

public void someVoidMethod(int i) {
  System.out.println("call method someVoidMethod");
}

public int foo() {
  int i = 5;
  return i;
}

Other useful resource

Chinese resource:

• 變異測試 (Mutation Test) — 一種提高測試和代碼質量的 ”新” 方法速記
• Test - 變異(Mutation)測試之你的測試到底是寫爽的，還是有效的?
• 突變測試的測試模式 - Mutation Testing in Patterns

English resource:

• Pitest resource
• An intro to Mutation Testing - or why coverage sucks
• Tests Coverage is Dead — Long Live Mutation Testing
• Start Killing Mutants: Mutation testing your code