Store file offsets in class variable, this way we won't lose them when running specs
Support RSpec idiomatic testing:
  expect("foo").to be_same_value_as <<-END
    foo
  END

  expect { "foo" }.to be_same_value_as <<-END
    foo
  END

  expect("foo").to be_same_value_as(log: 'test/logs/reference.txt')