Revise guidance on unit test to point people to object oriented test framework, rather than function based test framework

[rpurser47]

Our philosophy is to encourage the use of industry standard development workflows, and when it comes to tests, that's JUnit based object-oriented tests. While the functional test system is more approachable for MATLAB users unfamiliar with OO, it's definitely not industry standard, and so we should not be recommending it. Revise the guidance and find a tutorial to point people to.