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Lab 3: Testing

In this lab you will get familiar with different testing strategies and practice writing good unit tests in Java.

Concepts

Structural testing vs Specification testing: Two distinct types of unit testing are specification-based (historically: black-box) testing and structural (white-box) testing. Specification testing is when you write high-level test cases against the specification of a program, without using (or testing) the underlying implementation of the program. In structural testing, your tests are instead tailored to the specific underlying implementation of the code you are testing.

Code coverage: Coverage is the amount of code that has been executed by the tests. There are several coverage metrics, but one common metric line coverage is simply the percentage of lines (or statements) that have been executed by your unit tests.

Deliverables

  • Using specification testing, write tests for the LinkedIntQueue class, then execute them from within the IDE.
  • Use the above tests to find bugs in the ArrayIntQueue class.
  • Add tests to achieve 100% line coverage for the ArrayIntQueue class, and show coverage results in the IDE or as an HTML report.
  • Describe your experience with the tradeoffs between structural testing and specification testing to your TA. (No written answer is needed.)

Instructions

Setup

Fork and clone the repo from https://github.com/CMU-17-214/s24-lab03. The code is set up with JUnit. You can use your IDE to open the folder of Java and run the existing tests with the command in the readme.md. You can also see Appendix 1 for how to run tests in your IDE.

Testing

For the LinkedIntQueue class, use specification testing by refering to the IntQueue specification in IntQueue.java. Write additional tests and execute them from within the IDE.

For the ArrayIntQueue class, use structural testing. Specifically test the underlying implementation of the ArrayIntQueue class, not just test against the IntQueue specification.

  1. Open the Java folder with your IDE. Run the IntQueueTest class in the IDE (see readme.txt). Change the mQueue variable to ArrayIntQueue and run the tests again. Use your IDE to see the line coverage result. See appendix 3 for coverage tooling.
  2. Try to find two bugs in ArrayIntQueue by running your tests. Fix each bug that was found.
  3. Write more test cases to achieve 100% line coverage.

Appendix 1: Test Integration in VSCode

The Test Runner for Java plugin in VSCode provides great test integration functionality. The testing side panel shows all the tests of the current project. You can also run all tests or a particular test here.

lab03_test_side_panel

After running the test cases, the plugin also shows the failed test cases. Also, you can direct to the failed assertions, and VSCode can show the concrete reasons for the failures.

lab03_test_example

Appendix 2: Test Directories For Java

By convention in Maven, test files are placed in a test folder with the path src/test/java. You may need to create this directory if it does not exist. (This is useful for homework 2.) In some IDEs, you may need to indicate that this directory contains test files for the IDE to recognize and run the classes. In this directory create the same package structure as in src/main/java and place the test class in the same package as the class to be tested.

Appendix 3: Coverage Tools

In Java, we already set up the project to use Jacoco for collecting coverage information. If you run mvn test or mvn site to execute the tests, it will produce a report in target/site/jacoco/index.html. You can check the pom.xml file to see how we enabled this. Open with a browser to view the coverage report.

Your jacoco report should be similar to this when viewed in the browser. lab03_jacoco_report

In IntelliJ you can run tests with Coverage directly from within your IDE: Right click on test class and select Run '$classname' with Coverage; there should be a panel that pops up the right side of the screen showing class coverage.