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Lecture 02, Wed 01/05

Code Coverage and Mutation Testing (jpa01)

Programming Assignments

• jpa00 - Simple Java Hello World (using Maven, Java 17)
• jpa01 - Java OOP, Unit Testing (Junit 5), Code Coverage (Jacoco), Mutation Testing (pitest)
• jpa02 - Deploying Spring Boot Hello World on Heroku

See Gradescope for due dates.

Both jpa00 and jpa02 are self-explanatory, and don’t involve much other than following directions.

jpa01, on the other hand, requires some thought, and involves learning some new concepts.

So let’s dig in.

Today: preparation for jpa01

Today, we’ll discuss:

• Maven
• JUnit
• Jacoco (Code coverage)
• Mutation Testing

as background for jpa01.

Today will be an exception to the usual way the course works, in that we may end up using the entire time for a more “traditional lecture”; there’s a lot of ground to cover with these four topics.

We’ll use a series of tutorials that are available here, all based on a simple Java class callled Student

• https://ucsb-cs156.github.io/tutorials/

You are encouraged to work through tutorials 01 through 09 on your own at a pace suitable for you; our tour in lecture today will be super fast, as we have a lot to cover.

So if you are left a little bewildered, if it all comes too much too fast, don’t worry. Just let as much sink it as can sink in, then go back through it on your own.

Overview

• If you know what make and Makefiles do for C/C++ programming, that’s a good starting point for understanding the role of Maven in Java programming.
  • Note that it’s not a perfect analogy; make is imperative and tied to Unix commands, while Maven is declarative and platform independent
  • Maven also incorporates a package manager which plain vanilla make does not.
• JUnit is a framework for unit testing: writing tests that can be run to test your code.
  • Unit testing is foundational for modern software development
  • Unit testing means testing one unit (e.g. a single method) at a time.
  • Typically, other kinds of testing, such as integration testing and end-to-end testing are built on top of a unit test framework.
  • It allows us to build an “automated test suite” that runs every time we make a change to our code.
• Jacoco: is Java Code Coverage.
  • It allows us to check whether every line of code is covered by at least one test.
  • This is a “good start” for measuring the quality of a test suite
  • But it’s possible to cheat, and get 100% test coverage while doing little to no meaningful testing.
• Pitest is a Mutation Testing framework for Java
  • It is a better way of evaluating the quality of a test suite.
  • The idea: start with the assumption that your code is correct.
  • Then, create “mutant” versions of yoru code that are assumed to contain bugs
  • See whether your test suite “kills off all the mutants” (i.e. detects that they have bugs).
  • If any mutants survive, you might have a problem with your test suite, or your code.

The rest of the lecture will be demonstrating these ideas using the Student tutorial.