How often does this really come up? When I want to set up a global variable containing JSON, which doesn't come all that often, I just do something like:

const jsonFoo = `{"foo": "bar"}`

This is of course not possible with regexp, and global regexes are pretty common, so I don't think the two packages can be compared here.

Using consts was the solution that I was using before, though interpolating strings with varaibles can lead to code that is pretty ugly in my opinion. I could go back to using strings here, for example

    var test_cases [][]byte = [][]byte{
		util.MustMarshal(map[string]string{
			"email":    "fake@bar.com",
			"password": password,
		}),
		util.MustMarshal(map[string]string{
			"email":    email,
			"password": "fake",
		}),
		util.MustMarshal(map[string]string{
			"email":  email,
			"secret": "fake",
		}),
		util.MustMarshal(map[string]string{
			"email":    email,
			"password": password,
			"secret":   "fake",
		}),
	}

Where util.MustMarshal is just the panic on err wrapper mentioned, but I think string formatting is messier.

I agree that these funcs would have a very limited usecase, but I would also think that it is a relatively simple implementation that is not backwards incompatible. It would panic presumable on programmer error, and save other tools from needing to add it to their projects

I can see how it can be useful in some niche cases, but writing your own helper function is just a handful of lines. Backwards compatibility and simplicity are not the only factors for adding API to the standard library - see https://golang.org/doc/faq#x_in_std.

These are just my thoughts, though.