Integration tests over unit tests for web apps

For web applications, prefer integration/request tests over isolated unit tests:
- Test the full request/response cycle
- Catch issues with middleware, routing, authentication
- More confidence that the feature actually works

```ruby
# Good: Integration test
test "user can create a post" do
sign_in users(:alice)
post posts_path, params: { post: { title: "Hello", body: "World" } }
assert_redirected_to post_path(Post.last)
assert_equal "Hello", Post.last.title
end

# Unit tests are still valuable for:
# - Complex business logic
# - Edge cases
# - Performance-critical code
```