Calibrating the extruder is a crucial aspect of 3D printing with filament (FDM or FFF). If the extruder distributes too little material, the object will have holes or walls that are too delicate. On the other hand, if it dispenses too much material, it will create an issue called over-extrusion which will leave the piece with globs and strings, aka "Stringing".
The aim of the retraction test is to achieve a "cleaner" part without material residues in the movement areas of the hotend. The slicer parameters that influence this test are mainly speed and retraction distance.
This test should be carried out every time you print with a new material, as it provides one of the main printing parameter parameter of the filament i.e. the extrusion temperature. This test consists of a staggered part, in which the extrusion temperature will be varied progressively by 5 degrees. As each material has an optimum temperature, this test has different parts for different materials. These parts are practically the same, only the temperature range is different for an easier reading.
The purpose of this test is to adjust the amount of extruded plastic, that is to say, that the deposited material is the one we want at any given moment. It is performed to correct small variations in the diameter of the filament. The parameter that influences the flow is the so-called extrusion multiplier, with a calibration of this parameter you can solve the typical problems of under-extrusion or over-extrusion.