To check whether mass is conserved in this calculation, open up solutions. Go to Reports → Fluxes and then under options, check "Mass flow rate". Then select the one inlet and two outlets. We would expect the mass flux to sum up to zero (or extremely small).
As we can see from the window above, the mass fluxes add up to -2.624226e-07, which is very close to zero.
Inlet boundary conditions are checked during the calculations. As long as the surface monitor for average velocity has been turned on, the velocity at the inlet will be plotted. Below is the velocity profile at the inlet plotted during the calculation.
The profile matches our mathematical function for inlet velocity perfectly.