Suggestion #1.rb

it 'should do something' do
  on_failure warn_that "@foo shouldn't be nil" do
    @foo.should_not be_nil
  end
end

Suggestion #2.rb

it 'should do something' do
  explain_that "@foo shouldn't be nil" unless
    @foo.should_not be_nil
  end
end

Suggestion #3.rb

it 'should do something' do
  on_failure do
    @foo.should_not be_nil
  end.report "this message"
end

Suggestion #4.rb (Aslak)

it 'should do something' do
  lambda do
    @foo.should_not be_nil
  end.on_error "this message"
end

Suggestion #4a.rb (Matt)

it 'should do something' do
  @foo.should_not be_nil(:because => "we like our foos, we do")
end

Suggestion #5 (Rick DeNatale)

describe "calculator" do
  it "should add two numbers together" do
    expect_that "2 + 3 = 5" do
      Calculator.new.add(2,3).should == 5
    end
  end
end
 
# if the expectation failed then the message would be 'expected 2 + 3 == 5, but got 6'
# perhaps this could be altered/extended with a way to insert the actual result with something like...
 
describe "calculator" do
  it "should add two numbers together" do
    expect_that "2 + 3 = 5 but we got $ACTUAL" do
      Calculator.new.add(2,3).should == 5
    end
  end
end