What are the pros and cons of automated Unit Tests vs automated Integration tests?

Question

Recently we have been adding automated tests to our existing java applications.

What we have

The majority of these tests are integration tes

Answer 1

As many have mentioned, integration tests will tell you whether your system works, and unit tests will tell you where it doesn't. Strictly from a testing perspective, these two kinds of tests complement each other.

I can't see how adding a bunch more unit tests on individual classes would help. Wouldn't that make it harder to refactor as it's much more likely we will need to throw away and re-write tests?

No. It will make refactoring easier and better, and make it clearer to see what refactorings are appropriate and relevant. This is why we say that TDD is about design, not about testing. It's quite common for me to write a test for one method and in figuring out how to express what that method's result should be to come up with a very simple implementation in terms of some other method of the class under test. That implementation frequently finds its way into the class under test. Simpler, more solid implementations, cleaner boundaries, smaller methods: TDD - unit tests, specifically - lead you in this direction, and integration tests do not. They're both important, both useful, but they serve different purposes.

Yes, you may find yourself modifying and deleting unit tests on occasion to accommodate refactorings; that's fine, but it's not hard. And having those unit tests - and going through the experience of writing them - gives you better insight into your code, and better design.