When using QGIS 2.x I have used Topology checker to find gaps between polygons, crossing lines and duplicated points/vertex. I also liked that it shoved a list of errors where I could zoom into each error to fix it.
In version 3.0.3 I see that topology checker is running automatically and tells me at once when I put two point on top of each other.
How can I make it check for gaps? Is there somewhere to set the topology rules?