tests: don't have cargo install test tools

[martinvonz]

I noticed that cargo install --path . will install the new fake-editor and fake-diff-editor binaries. We don't want that, so let's move them into a separate crate. The tests still find them without needing any modification.

Checklist

• [x] I have made relevant updates to CHANGELOG.md

[martinvonz]

FWIW git-branchless puts helper binaries behind a feature flag which isn't enabled by default:

https://github.com/arxanas/git-branchless/blob/3595f3d151dffb974f7f6fddb500c79ee25a0431/git-branchless-lib/Cargo.toml#L25-L36

What enables the integration-test-bin feature?

[arxanas]

@martinvonz Me manually passing --feature integration-test-bin 😊

I guess what we're doing is different. Your binaries are supporting the relevant tests, but my binaries are the tests.

[martinvonz]

@martinvonz Me manually passing --feature integration-test-bin 😊

I see. I'd really like to avoid having to do that, especially since every developer would need to remember to do the same. Maybe there's just no good solution until https://github.com/rust-lang/cargo/issues/3670 has been fixed. I guess the problem is effectively the same as with using e.g. the git binary in tests. The difference is just that the binary can be built by cargo.

[martinvonz]

Due to a recent build of jj, I'm now a proud owner of the fake-editor and fake-diff-editor binaries on my machine 😊

Sorry :( I don't know what the right solution to this problem is. I suppose we will also need a git binary on the path for tests in not too long (for running a git server to testing push/pull with, and to test GC, neither of which libgit2 supports AFAIK). For git, we can look for it on the path and have a $TEST_GIT override like I think git-branchless has. That doesn't work as well for these fake-* binaries, though.

[ilyagr]

I ran into this when I tried to make jj installable with cargo binstall[^1].

The approach suggested in https://github.com/rust-lang/cargo/issues/2911#issuecomment-1483256987 seems somewhat promising, unless you've tried it already or it seems too hacky.

[^1]: For my own future reference, the magic incantantion for binstall seems to be --pkg-url="{ repo }/releases/download/v{ version }/jj-v{ version }-{ target }.{ archive-format }". Using jj instead of jj-cli is necessary. It's a bit surprising that I needed to add v before versions.