I disagree, I actually think that in many cases asserts are easier than tests, and many people derive tests from assertions in their head (or use a tool like qu

I disagree, I actually think that in many cases asserts are easier than tests, and many people derive tests from assertions in their head (or use a tool like quickcheck which does it too). Unfortunately, there is too much focus on testing in today's software that tools for assertions are not on the same level as tools for testing. One class of assertions is type checking, but you can also have dynamic assertions while the code is running. OTOH, abstractions are harder, but it only takes one person to invent a good abstraction that covers a huge class of bugs, and others can copy it. Examples of good abstractions that prevent many bugs are arrays with bounds checking, garbage collection, or optional data type.