macOS test changes

tests/zfs-tests/include/libtest.shlib

@@ -1066,13 +1066,16 @@ function set_partition
 		fi
 
 		typeset bytes
-		bytes=size_mb * 1024
+		((bytes = size_mb * 1024))
 
 		# Dont create zero sized partitions
 		[[ $bytes == 0 ]] && return 0
 
 		# Convert to a sector count
-		typeset sectors=$(( $bytes / $sector_size ))
+		typeset sectors=$((bytes / sector_size))
+
+		# Make sure we have a gpt
+		gpt show $disk | grep -q GPT || gpt create $disk
 
 		# Add partition as "ZFS" - hopefully prevent DiskArbitrator popup.
 		log_must gpt add -s $sectors -t "6A898CC3-1DD2-11B2-99A6-080020736631" $disk
@@ -1144,6 +1147,14 @@ function delete_partitions
 				log_fail "Partitions for ${disk} not deleted"
 			fi
 		done
+	elif is_macos; then
+		for disk in $DISKSARRAY; do
+			if gpt destroy $disk; then
+				log_note "Partitions for ${disk} deleted"
+			else
+				log_fail "Partitions for ${disk} not deleted"
+			fi
+		done
 	fi
 }