This isn't specifically animal testing, rather it is a process to get life saving medicine. They are working hard to synthesize it luckily. This has been the subject of a few major podcasts but I can't remember which ones.

First off, this isn't testing. We know exactly what we need Horseshoe Crab blood for, and it's incredibly important.

Second, it's probably not torture. The worst-case-scenario level of discomfort from bleeding them is fairly low, like a human giving blood. And that (incorrectly) presupposes them having as advanced pain-sensing as humans. The actual death rate is the bigger issue, but we are talking about saving lives and the medical community is trying really hard to change the status quo on this. Covered below.

Third, what you're seeing in that picture saves thousands of lives per year. How much human suffering, how many human deaths, are you willing to accept to achieve those goals? What if one of those humans that has to suffer or die was your kid? There's no plant-based alternative to this process at this time.

Let me clarify this. Using horseshoe crabs for this purpose is VERY EXPENSIVE. It's only done because we don't have an alternative yet, and the process is necessary for modern medicine. There is plenty of research going into either making this process less expensive (which probably involves a lower death rate for crabs) or finding an entirely different process to achieve the same goals. But none has been found (well, except that they used to use rabbits for this. I don't know the details)

I can understand the desire to spare... um...shellfish some..uh.. pain I guess. But NOT at the expense of human life and suffering. That's just silly.