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DevOps-M4: Incremental Testing Toolkit

This is the repository for DevOps special milestone. We built an incremental testing toolkit to achieve test priority purpose. And we use solar-calc as our node.js application.

  • Node.js application: link
  • Screencast: link


In the traditional testing technique, the testing team will run every test case in the test suite to make sure the code is robust and deliverable. However, in many times, running all test cases is time-consuming, especially for some complex projects.

Here we introduced a tool to perform the incremental testing. At each time the code wants to merge to the master branch of remote code repository, our tool will analysis which part of the code is modified, comparing to the existed delivered code via git diff. Then our tool analysis which test cases should or should not be tested. One test case might not be tested since, according to the history record, it did not touch the modified code.


  • When testing the project, determine which tests case are unnecessary and skip those cases.
  • A test case is no need to test when its covered statements did not appear in git diff.


The image above presents the workflow of the incremental testing toolkit. When developers try to commit their modifications, our toolkit will check the difference between current work directory and last or previous commit via git diff command. Then the toolkit finds the touched lines of code, in other words, modified lines of code. According to line modification information, the toolkit looks for the corresponding methods. In the meanwhile, the toolkit has already parsed all existing test cases and found out the touched methods by each test case. The last step is to run only certain test cases instead of the whole test suite.

Technique Summary

  • We used the diff tool provided by git to find the changes between current work directory and last or previous commit.
  • Our analysis unit is the function and we designed this incremental testing toolkit to handle the inner function modification. That is, for one test case, if all of its covered function are not changed in the new commit, it won't be run. On the contrary, it will be tested.
  • We used the JS code coverage tool istanbul to find which statements one test is covered. Then we wrote scripts to find out which functions these statements are belong to.
  • We implemented the visuzlization tool mochawesome to show which test cases are actually tested for the modifications in current work directory.

Technique Details

File Structure

├── checker
│   ├── changed_method_comparator.js
│   ├── commit_changed_method_finder.js
│   ├── get_testcase_id.js
│   ├── git_diff.js
│   ├── method_finder.js
│   ├── package.json
│   ├──
│   ├── test_covered_method_finder_legacy.js
│   └── test_separator_legacy.js
├── images
│   ├── M1-4 workflow.png
│   └── M4-workflow.png
├── pre-commit
├── results
│   ├── commit_changed_method
│   ├── commit_touched_testcases
│   ├── commit_touched_testcases_desc
│   ├── test_case_desc
│   ├── test_covered_method_legacy.csv
│   └── test_covered_methods.json
└── test_covered_method_finder
    ├── Gemfile
    ├── Gemfile.lock
    └── test_covered_method_finder.rb
  • Folder checker stores the majority of scripts for incremental testing toolkit.
  • Script changed_method_comparator.js reads the changed methods information from commit_changed_method, finds the corresponding test cases from test_covered_methods.json and writes the filenames of test cases into commit_touched_testcases file.
  • Script commit_changed_method_finder.js requires git_diff.js, finds the commit changed methods by calling method_finder.js.
  • Script get_testcase_id.js gets the test case filenames from commit_touched_testcases, uses test case descriptions in the format of test desc 1|test desc 2|test desc 3 and writes into file commit_touched_testcases_desc. The bar-separated format is used for mocha grep option.
  • Script git_diff.js is able to find the changes between current work directory and last or previous commit.
  • Script method_finder.js requires esprima to generate AST tree, and finds methods by offering filename and certain line number.
  • Script test_covered_method_finder_legacy.js and test_separator_legacy.js are two legacy scripts not been used any more.
  • Folder images stores images.
  • Script pre-commit is a git hook aiming to trigger incremental testing toolkit and a serious of jobs.
  • Folder results stores all intermedia and final results
  • File commit_changed_method records filename and method names about the modifications of current work directory.
  • File commit_touched_testcases stores corresponding test cases of methods mentioned in commit_changed_method.
  • File commit_touched_testcases_desc records test case descriptions of test cases stored in commit_touched_testcases.
  • File test_case_desc documents descriptions of all test cases.
  • File test_covered_methods.json logs relationships between test cases and methods in the structure of filename => method name => {test case1, test case2} .
  • File test_covered_method_legacy.csv records above relationships in a deprecated data structure.
  • Folder test_covered_method_finder stores ruby script to generate test_covered_methods.json and update this file during each commit.

pre-commit git hook

Below is partial content of this git hook:

echo '=====Step1. Find changed methods=========='
node ./commit_changed_method_finder.js

echo '=====Step2. Find touched testcases=========='
node ./changed_method_comparator.js

echo '=====Step3. Get Desc ID corresponding to testcases=========='
node ./get_testcase_id.js
cd ..
CMD=`cat ./results/commit_touched_testcases_desc`
echo $CMD
A="mocha test/test.js -g \"$CMD\" --reporter mochawesome"
eval $A
echo '=====Step4. Update test covered methods=========='
cd $DIR_M4
cd ./test_covered_method_finder
ruby test_covered_method_finder.rb

Basically, this hook executes four steps:

  • The first step is to find the changed methods by executing commit_changed_method_finder.js script.
  • The second step is to find the touched test cases according the results of last step and running changed_method_comparator.js script.
  • The third step is to obtain the descriptions of test cases by running get_testcase_id.js and generate report via mochawesome.
  • The last step is to update test_covered_methods.json by executing test_covered_method_finder.rb ruby script.

Below is the screenshot of report generated by mochawesome with all 30 test cases being ran originally.

Below is the screenshot of terminal output of pre-commit hook.

Below is the screenshot of report generated by mochawesome with only 2 out of 30 test cases being run by implementing our incremental testing toolkit.

Incremental Testing Toolkit in Whole Pipeline

This the workflow of the whole pipeline. As you can see our incremental testing toolkit actually occurs before the first milestone. And it executes test cases with higher priority, which saves developers lots of time. And the benefit will be more obvious when implementing out toolkit in a larger project with more test cases.


[1] Jiang, Bo, et al. "How well does test case prioritization integrate with statistical fault localization?." Information and Software Technology 54.7 (2012): 739-758.

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