Normal:

describe "When reading past last character in the string" do
  before(:each) do
    @string_reader = StringReader.new("ab")
    @string_reader.read
    @string_reader.read
  end

  it "should asplode!" do
    lambda{@string_reader.read}.should raise_error
  end
end

Desired:

describe "When reading past last character in the string" do
  before(:each) do
    @string_reader = StringReader.new("ab")
    @string_reader.read
    @string_reader.read
  end

  it "should asplode!" do
    running{@string_reader.read}.should raise_error
  end
end