disposing a flow measuring sub in a drill string of the wellbore, wherein the flow measuring sub mechanically connects a drill pipe joint and a drill pipe of the drill string;

sustaining, using a mud pump, a fluid flow downstream along an annulus and upstream along the drill pipe, wherein the annulus is formed between the drill pipe and a casing string of the wellbore, wherein the fluid flow reverses direction through an open port in a wall of the drill pipe or an open end of the drill pipe, wherein the fluid flow returns to a mud tank from the drill pipe through the flow measuring sub and the drill pipe joint;

generating, using a measuring device of the flow measuring sub, flow measurement data of fluid movement through the flow measuring sub for sending to a computer device of the flow measuring sub; and

determining, using the computer device and based at least on the flow measurement data, a success/failure result of the inflow negative test.