Exactly what is integration testing - compared with unit

Question

I am starting to use unit testing in my projects, and am writing tests that are testing at the method/function level.

I understand this and it makes sense.

But,

Answer 1

Here are a couple of constraints that a good unit test satisfies. Meeting these constraints also required good testable code.

1. No I/O - disk or network
2. Only one assertion (if multiple, they should be minor variations of each other)
3. Does not exercise (cover) much more production code than what it asserts

These constraints usually don't apply to integration tests.