This model allows you to quickly test if your filament flow rate is correct.  It is set up for a layer height or 0.2mm and a line width of 0.44mm. The .step file is included if you want to modify this model for your specific uses.

The single base layer lets you easily see if you are under extruding your filament and leaving gaps.  The walls of the square allow you to easily measure the wall thickness using a caliper for 1, 2, and 3 lines thick.  The round 2 line thick cylinder around the square lets you easily see if the lines are adhering in all X,Y directions.  A simple squeeze is a good test to make sure the walls are truly bonding.