In the recognise test convert some ST1 multiple structure to ST1 single structure to test the isST1SingleOpcode() function. This was found to be uncovered in a recent code coverage report.
I had thought I had covered the ST1 single structure form by putting just one register in the argument list (st1 {v0.16b}, [x1], x2), however it turns out that I needed to use a different syntax (st1 {v0.b}[1], [x1], x2).