PHPUnit Test Question - How to Unit test my class

[haobangxiong]

I'm trying to get into Unit testing for the obvious positives it introduces, and I'm trying to write a Unit test for a class I wrote the other day. (I know this is the opposite to TDD, please bear with me)My class, \[code\]Image\[/code\], is used in conjunction with some others for image manipulation. \[code\]Image\[/code\] essentially wraps a GD image resource and stores data along with it. For example, an instance of \[code\]Image\[/code\] will always contain it's current state, i.e. its new width/height if resized, the original image data, etc.The \[code\]Image\[/code\] class also contains methods for,

• Creating itself from a file, string data, or URL, e.g. \[code\]$image->loadFromPath()\[/code\]
• Creating a new GD image resource from the properties of the current \[code\]Image\[/code\] instance, e.g. for image resizing to maintain background transparency, etc.
• Cloning the GD image resource for use in the manipulation classes

What I'm struggling with is how to Unit test this class properly with PHPUnit. I've done some reading and I have a few conflicting ideas on how to approach it and I don't know what's right. Do I,[*]Write a test for each method of the class. I read somewhere that I should test each and every method. However, some of the methods run others (rightly so may I add), so you then have a chain of dependency. But I also read that each Unit test should be independent from the other. So what do I do if this is the case?[*]Write each test as a usage route of the class. I also read somewhere that each test should instead represent 1 path/usage route you can take with the class. Therefore if you cover every usage, you'll ultimately get complete code coverage.So, which of these is correct, if any?