I created a plugin for groovy/grails projects that takes this principle to the next level called "build-test-data". In grails, domain objects have constraints on them that determine which fields are required and what kinds of validation they need in order to be persisted.
The plugin adds a "build" method on all domain objects that will create and save a new instance of a domain object with all required fields populated with dummy data. You can then pass in any fields that you actually want to have specific values that matter to your test.
It turns your example above (groovy style code) from this:
Posting.build(
title: "irrelevant title",
content: "irrelevant content",
queuedAt: null,
published_at: null
)
Into this:
Posting.build()
You don't have to specify any values that you don't care about, it populates title, content, queuedAt, and publishedAt for you. If you did care about the title in your test, you'd just use:
Posting.build(title: "title that matters for test")
I'm not aware of any other rails/django/merb type frameworks with this addition to their testing frameworks, but I think it'd be possible to create something similar for all of them. With rails active record interrogation of the database constraints, it should be possible to do the same kind of thing.