ellipse bz 0 0 0 0 0 1 1 .5
convert bz bz
mkedge e1 bz 0 1
mkedge e2 bz 1 2.5
mkedge e3 bz 2.5 6
wire w e1 e2 e3
getanacurve c w ell 1.e-7
if {[isdraw c]} {
  set log [dump c]
  if { [regexp {Ellipse} $log ] != 1 } {
     puts "Error: curve is not an ellipse"
  }
} else {
  puts "Error: required curve is not got"
}