Chapter 4  Column gaps and rules  4.1 ‘columngap’
Go to the relevant page of the specification.
 multicolgap000 (ahem)

columngap (basic)
This test checks that column gap appears between two columns.  multicolgap001 (ahem, may)

'columngap: normal'
This test checks that the 'normal' column gap is 1em, which is suggested  and not prescribed  by the specification.  multicolgap002 (ahem)

columngap (basic)
 multicolgap003 (ahem, may)

'columngap: normal'
 multicolgapfraction001 (ahem)

'columngap' with increasing values
 multicolgaplarge001 (ahem)

'columngap' with large value
This test checks that when 'columngap' is large and when used 'columnwidth' is narrow, then content extends into columngap until its middle and content can extend, overflow outside the edges of the multicolum element if 'overflow' is set to 'visible'.  multicolgaplarge002 (ahem)

'columngap' with large value
 multicolgapnegative001 (ahem, invalid)

columngap with negative value
 multicolheight001 (ahem)

columncount and height
This test checks that length of column rules is equal to the length of the columns and if a nth column box overflows outside the available width of a multicolumn element, then an (n1)th column rule should be drawn. In this test, a 3rd column box is created outside the content edge of the multicolumn element: therefore, a 2nd blue column rule should be drawn accordingly.