tests: don't have cargo install test tools

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.

Cargo.toml

@@ -17,20 +17,12 @@ categories = ["command-line-utilities", "development-tools"]
 name = "jj"
 path = "src/main.rs"
 
-[[bin]]
-name = "fake-editor"
-path = "testing/fake-editor.rs"
-
-[[bin]]
-name = "fake-diff-editor"
-path = "testing/fake-diff-editor.rs"
-
 [[bench]]
 name = "diff_bench"
 harness = false
 
 [workspace]
-members = ["lib"]
+members = ["lib", "testing"]
 
 [dependencies]
 assert_cmd = "2.0.4"

testing/Cargo.toml

@@ -0,0 +1,24 @@
+[package]
+name = "jujutsu-testing"
+version = "0.4.0"
+authors = ["Martin von Zweigbergk <martinvonz@google.com>"]
+edition = "2021"
+rust-version = "1.57"
+license = "Apache-2.0"
+description = "Library for Jujutsu (an experimental VCS)"
+homepage = "https://github.com/martinvonz/jj"
+repository = "https://github.com/martinvonz/jj"
+documentation = "https://docs.rs/jujutsu"
+readme = "../README.md"
+
+[[bin]]
+name = "fake-editor"
+path = "src/fake-editor.rs"
+
+[[bin]]
+name = "fake-diff-editor"
+path = "src/fake-diff-editor.rs"
+
+[dependencies]
+clap = { version = "3.1.10", features = ["derive"] }
+itertools = "0.10.3"