  This contribution intends to give a pedagogical introduction to the topic of
dark energy (the mysterious agent supposed to drive the observed late time
acceleration of the Universe) and to various observational tests which require
only assumptions on the geometry of the Universe. Those tests are the
supernovae luminosity, the CMB shift, the direct Hubble data, and the baryon
acoustic oscillations test. An historical overview of Cosmology is followed by
some generalities on FRW spacetimes (the best large-scale description of the
Universe), and then the test themselves are discussed. A convenient section on
statistical inference is included as well.
