Cotta-asserts is a public release of the JUnit 4 assertion adapter that came to as part of the Cotta implementation and my search for a better sematics for assertions in test.
FEST-Assert is a Java library that provides a fluent interface for writing assertions. Its main goal is to improve test code readability and make maintenance of tests easier.
- Cotta-asserts: http://cotta.sourceforge.net/assertions.html
- FEST-assert: http://fest.easytesting.org/assert/wiki/pmwiki.php
The bottom line is that these two libraries are trying to solve the same problem in a different way, so they are both viable solution for writing assertions through fluent interface. Even though personally I like what I have built, I would not argument very hard about using one versus the other, same way as I would never argue between JUnit and TestNG, even though all my projects have been JUnit (And I know some people feel strongly about it).
I can also say the same thing about Java versus Ruby. When it comes to the bottom line, having a gelling team building high quality software that makes the user happy is all I care.
Why I like FEST asserts
Don't get me wrong, I love FEST asserts. Their API looks solid and really complete. Even now, Cotta Asserts still has some way to go to catch up, it is simply not high enough on my list, and I have not found anyone willing to contribute.
Why I like Cotta Asserts
With that said, I think it is worth it to write down the reason that I like Cotta Asserts.
First of all, Cotta Asserts is aimed to filling the gap of JUnit and Hamcrest, nothing more. It is just an API adapter that exposes the assertThat method in JUnit 4 and the matcher classes in Hamcrest. If one day this fluent API appears on the new JUnit release, I would be happily retire this little side project, and get back to the next item of my long list of things I would like to try as an open-source project.
Second, you can extend Cotta Assert however you want it to be, because all the classes are open to extension. You can extend AssertionFactory and add more methods to return other assert objects. You can make your AssertionFactory return different StringAssert.
For FEST-asserts, I always wonder why they made the classes final. It does not seem to serve any purpose. Then again, I never asked, so there could be some good reason behind it.
If you have been using assertThat method in JUnit, chances are that you already have a bunch of matchers lying around, and probably start having trouble remembering where they are. You just need to create your AssertionFactory and Asserts to leverage them and you don't have to throw anything away or even change anything.
With FEST-asserts, when you look at an API like this, something is just not right...
FEST-asserts requires you to add one assertThat method for each object type that you want to run asserts on, and one method for each custom condition. It can get confusing sometimes if you have different modules that do assertion on different objects in the module.
With Cotta Asserts, you only need one field declaration from the super test case class, and everything just goes from there. So it is really easy to set up, and really easy to customize it so that each module can have methods that only create asserts that are applicable to the module.
So here you are, happy testing!