Two Point Loads at One Third Points on a Simple Beam
First,is the beam strong enough that it doesn't fail by the fibers on the bottom being torn apart, a fiber failure.
Second, is the beam stiff enough that there will not be excessive deflection. A bouncy floor, cracked tile or plaster would be examples of this.
Third, is the beam strong enough that its fibers don't slip past one another, bend a magazine and watch the pages slide past one another. This is a horizontal shear failure.