GGACR/I-No/Matchup/Testament

The General Gameplan

Look for opportunities to punish him setting up traps at the wrong time via HCL. I-No is quite effective at dealing with Testament's traps.
Also look for situations where you can get his normals to whiff so you can whiff punish (such as with empty jump > dive), and try to directly challenge normals where possible (go under them with STBT for example).
Use Momentum Carry HCL more frequently in this matchup to bait his full body counter that otherwise beats it (the forward movement will dodge it and set up a punish, if he doesn't FRC). It can also help you close the distance to punish trap-setting attempts that the other player thinks are far enough away to be safe.

That's... about it? If you retreat to full screen, EXE Beast still tracks your location and he has time to set traps. If you get in his face and lose initiative, you're in a very bad position. At entry level, I-No has all the tools to harass and mess up Testament. Once you're fighting a really strong Testament you need a lot of hitbox and frame knowledge to understand what your escape options are and what his counterplays are, so that once you fail at neutral (and you will due to Testament's tools allowing him to create straight guessing situations for I-No in neutral) you haven't already lost.

The problem is that his normals are very difficult for us to challenge (typically involves guessing and committing), his pressure is difficult to escape safely once he gets you to block, and risk/reward can swing wildly into his favor when poison is involved.

Look for opportunities to Dead Angle and Burst to escape pressure so you don't have to sit in blockstun all game. Even though his mixup isn't as dangerous as Eddie, and his pressure doesn't deal chip damage the way Venom does, the longer you let him set up the more burst potential he has. You don't want to get opened up once by throw, poisoned, and lose 80% of your health to what would otherwise be a low-damage throw combo from any other character... or from any starter really. And worse - even if you escape, you could be escaping into a trap, or trading in his favor due to a trap activation giving him a confirm anyway.

TL;DR: Try to give him as little time to set up as possible, and use I-No's strengths (explosive damage and extremely difficult to block mixup) to win without letting him play the game.

What your opponent Can Do

Testament has the combination of incredible disjointed normals, stage control via traps (that also protect him while he's blocking and can let him convert in situations where other characters get nothing), poison to compensate for low average damage (which can actually create situational TODs), a full-body counter that causes poison and can be FRC'd to make it safe, a teleport, a curse that summons his familiar to harass you in neutral (including a force break that applies the curse on block), extra normals with good gatling routes, an extra standing overhead (his 6P), a forward moving ground normal with invul frames (his 2H), a super that buffs his traps, another super set on a delay (to control space) that applies poison, a delay-able ground special that let's him reset his ground pressure (which can be done safely via an FRC), and long-duration combo routes that are perfect for dealing lots of poison damage over time, and also for stalling until the meter gain proration from using an FRC has gone away, so that he always has meter to use on all of the above tools.

You don't really even need to break down what about the above is good. He has a little bit of everything and is considered to be a top 3 character for a reason. His weaknesses include:

A lack of frame advantage on his normals (when he has tons of gatling and special cancel options to punish you for acting when you think he's done with his string).
Air normals that do not hit below him by a significant amount.

Good luck with that.