I agree with jimc 100%. If you are seeing gaps between your perimeters, then you need to adjust your extrusion multiplier. There's nothing wrong with how the software is slicing the parts, you just don't have your extrusion rates dialed in yet.
There really isn't any special part that is needed for this. Just pick any cube and set number of perimeters to 1, use 0 top and bottom solid layers, and 0% infill. That will create a single outline print of the cube. Then you can measure the thickness of the walls. Increase your extrusion multiplier until the measured thickness matches the "extrusion width" value that you specified in your slicing settings.
Once they match, it would probably be useful to print the same cube, but now use 3 or 4 perimeters just to verify a real-world scenario. Make any final minor adjustments that are needed, and then you are good to go!