This tool is designed to measure the observability features of mutation testing at the method level. In another word, you can learn how hard to achieve 100% mutation score of each method in your project.

The mutation_observer package is build with maven. Install maven and do:

mvn package

This will produce a target directory with the following two jars:

• mutationObserver-1.0-SNAPSHOT.jar: This is the standard maven packaged jar
• mutationObserver-1.0-SNAPSHOT-jar-with-dependencies.jar: This is an executable jar which includes the mutation mutation observer

The current version of mutation_observer can only work with maven project. Before running mutation_observer, you need to compile and test the target project (mvn test) and obtain the PiTest mutation result for your project. The PiTest mutation result must in csv format. You can achieve that with outputFormats in Pitest plugin:

<plugin>
     <groupId>org.pitest</groupId>
     <artifactId>pitest-maven</artifactId>
     <version>1.4.0</version>
     <configuration>
         <skip>false</skip>̨
         <outputFormats>
            <outputFormat>CSV</outputFormat>
         </outputFormats>
     </configuration>
 </plugin>

To run mutation_observer, you need to specify four parameters:

• project_name: project name
• project_dir: project directory
• PiTest_file_path: the file path for PiTest mutation results (in csv format)
• output_file_path: file path for output results. This parameter is optional. If this parameter not specified, the output file will be in the current dir with name of [project_name]_mutation_observer_all_results.csv).

java -jar mutationObserver-1.0-SNAPSHOT-jar-with-dependencies.jar [project_name] [project_dir] [PiTest_file_path] <output_file_path>

The output csv file contains 21 columns:

• method_name: method name
• is_public: whether the method is public or not
• is_static: whether the method is static or not
• is_void: whether the return value of the method is void or not
• is_nested: whether the method is located in a nested class or not
• method_length: the number of lines of code in the method
• kill_mut: the total number of mutations killed for this method
• total_mut: the total number of mutations generated from this method
• nested_depth: the maximum number of nested depth
• direct_test_no: the number of methods directly invoked by the test methods
• test_distance: the shortest method call sequence required to invoke the method in test methods
• void_no: the number of void methods in the class where the method located
• getter_no: the number of getter methods in the class where the method located
• total_method_no: the total number of methods in the class where the method located
• method_sequence: the text representation of control-flow sequence for this method, e.g., (root(cond))
• (cond): the number of conditions (if, if-else and switch) in the method
• (cond(cond)): the number of nested conditions (e.g. if{if{}}) in the method
• (cond(loop)): the number of nested condition-loops (e.g. if{for{}}) in the method
• (loop): the number of loops (for, while and do-while) in the method
• (loop(cond)): the number of nested loop-conditions (e.g. `for{if{}}}``) in the method
• (loop(loop)): the number of nested loop-conditions (e.g. for{for{}}) in the method

You can learn how to use mutation_observer by following the example here step by step:

1. first download mutation_observer via GitHub repository:

git clone https://github.com/qianqianzhu/mutation_observer.git

2. compile mutation_observer with maven:

cd mutation_observer
mvn package

3. execute mutation_observer with example project testProjec:

java -jar mutationObserver-1.0-SNAPSHOT-jar-with-dependencies.jar testProject ../src/test/test_resources/ ../src/test/test_resources/testProject/target/pit-reports/201901170312/mutations.csv

4. Now you can find the output file in your current directory testProject_mutation_observer_all_results.csv:

method_name;is_public;is_static;is_void;is_nested;method_length;kill_mut;total_mut;nested_depth;direct_test_no;test_distance;void_no;getter_no;total_method_no;method_sequence;(cond);(cond(cond));(cond(loop));(loop);(loop(cond));(loop(loop))
org.testproject.A:methodA;true;false;true;false;3;0;1;0;2;1;5;0;5;(root);0;0;0;0;0;0
org.testproject.A:methodB;true;false;true;false;3;0;1;0;0;2;5;0;5;(root);0;0;0;0;0;0
org.testproject.A:methodC;true;false;true;false;4;0;2;0;0;2;5;0;5;(root);0;0;0;0;0;0
org.testproject.A:methodD;true;false;true;false;3;0;1;0;1;1;5;0;5;(root);0;0;0;0;0;0
org.testproject.A:methodE;true;false;true;false;3;0;1;0;0;3;5;0;5;(root);0;0;0;0;0;0