Alonso left Formula 1 at the end of the 2018 season after spending four years with McLaren. The Spaniard joined McLaren after failing to pick up a championship with Ferrari.
However his time at McLaren failed to produce strong results as it struggled with former engine supplier Honda. After switching to Renault in 2018, it was still not able to produce convincing results.
The lack of competitiveness and lack of battling in the midfield left Alonso to take the decision to depart F1 after 17 years.
Alonso will drive for one and a half of the two days of running, alongside compatriot Carlos Sainz who is racing full-time for the Woking squad in 2019.
The double world champion will jump behind the wheel on Tuesday for the whole day before driving the car once again in the afternoon on Wednesday.
Bahrain International Circuit - Winter testing