Star halfback Shaun Johnson says the Kiwis are preparing for their first true test against a battle-hardened Tongan side in Saturday's Rugby League World Cup clash in Hamilton.

The Kiwis swept past Scotland 74-6 in Christchurch on Saturday for their second straight victory, but getting past Tonga looms as a much more difficult assignment after they overwhelmed Samoa 32-18 at Waikato Stadium.

The two sides will face off to decide who finishes the top of Pool B to book a quarter-final match-up against the third-ranked side from Pool A, while the runner-up will likely meet Pool D frontrunners Fiji.

Johnson - who bagged a try and nine goals against the Bravehearts to eclipse former Kiwis captain Matthew Ridge's record to become New Zealand's highest pointscorer - says the Kiwis expect their defence, and their mettle, to be put under greater scrutiny than they have been throughout the opening fortnight of the tournament.

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"We haven't been out under as much pressure as what we'd have liked to because when you get momentum it's really easy to carry it on and it just snowballs," said Johnson in reference to their 14-tries-to-one demolition of Scotland.

"The true test is when we get put under pressure so this week we will at some point for sure and it's how we respond to that.

"We let in a try last night which we were pretty disappointed about. We let one in again late against Samoa which we were filthy about - just those little areas about finishing the job off and getting it done properly.

"There's always room for improvement but the true test is going to be when we are put under pressure."

The match promises to be a blockbuster after four former Kiwis - Jason Taumalolo, Manu Ma'u, Sio Siua Taukeiaho and David Fusitu'a - opted to switch allegiances and play for Tonga, but Johnson downplayed the likelihood of fireworks erupting between the two sides.

"Maybe for you guys, for the media (there's added spice)," he said.

"It's a headline isn't it? But for us, they've got Tongans playing for Tonga and we've got Kiwis playing for New Zealand. It's as simple as that.

"They've got some really high calibre players and everyone in their team is from either the NRL or Super League so it's going to be an awesome challenge. I can't wait."

With just over 18,000 fans - predominantly Tongan supporters - turning out to see the two Pacific island nations square off, Johnson understands New Zealand supporters are likely to be in the minority this weekend.

"I would love to stand here and be confident that our supporters are going to outshine theirs but I've seen firstly what Samoan fans can do, and watching the game last night, what Tongan fans bring as well.

"We'll roll in there and bunker down and look to get the job done."

Johnson was reluctant to dwell on his pointscoring milestone saying he and his teammates are focusing on the bigger picture.

"It's obviously pretty cool to be recognised alongside Matthew Ridge and those sorts of players.

"It's something I'll definitely look back on once my career is all said and done.

"There's a much bigger goal here that I and the team want to achieve. As long as we stay on track and do that I'll be happy with that."