1.rb

class PostTest < ActiveSupport::TestCase
  test "adds 20 points to post author" do
    @post.save!
    assert 20, @post.author.points # should be assert_equal
  end

  should "add 20 points to post author" do
    @post.save!
    @post.author.points == 20 # no assertion, should be "@post.author.points.should == 20"
  end
end

2.rb

class PostTest < ActiveSupport::TestCase
  def setup
    @post = Post.make # "generic" post
    @old_post = Post.make(:created_at => 1.year.ago)
    @reported_post = Post.make.tap(&:report)
  end

  # ...
end

3.rb

class PostTest < ActiveSupport::TestCase
  def setup
    @post = Post.make_unsaved
  end

  test "reporting posts" do
    @post.report! # saves and reports the post when needed
    assert @post.reported?
  end

  # ...
end

4.rb

class PostTest < ActiveSupport::TestCase
  def self.startup
    @@author = User.make
  end

  def setup
    @post = Post.make_unsaved(:author => @@author)
  end

  test "saves successfully" do
    assert @post.save
  end

  test "can be reported" do
    @post.save
    assert @post.report
  end

  # ...
end

5.rb

module RemovableTests
  def test_sets_removed_at_attribute
    @model.remove
    assert @model.removed_at
  end
end

class PostTest < ActiveSupport::TestCase
  include RemovableTests

  def setup
    @post = @model = Post.make_unsaved
  end

  # ...
end

I find 1.rb to be more of a problem with Test::Unit than RSpec. In Rspec, everything you write, ends in .should . While of course you could leave it off by accident, once you write a few RSpec tests, it rarely happens again. I did the assert vs. assert_equal thing all the time.