tests: split lib/tests to separate create

This breaks dev-dependency cycle: jj-lib -> testutils -> jj-lib.

I put Cargo.toml in lib/tests so the directory structure looks familiar. I'm
not sure if this layout is common, but I found this pattern in gix.

Cargo.toml

@@ -2,7 +2,14 @@ cargo-features = []
 
 [workspace]
 resolver = "2"
-members = ["cli", "lib", "lib/gen-protos", "lib/proc-macros", "lib/testutils"]
+members = [
+    "cli",
+    "lib",
+    "lib/gen-protos",
+    "lib/proc-macros",
+    "lib/tests",
+    "lib/testutils",
+]
 
 [workspace.package]
 version = "0.24.0"

lib/Cargo.toml

@@ -16,15 +16,11 @@ include = [
     "/LICENSE",
     "/benches/",
     "/src/",
-    "/tests/",
     "!*.pending-snap",
     "!*.snap*",
 ]
 
 
-[[test]]
-name = "runner"
-
 [[bench]]
 name = "diff_bench"
 harness = false
@@ -92,7 +88,6 @@ num_cpus = { workspace = true }
 pretty_assertions = { workspace = true }
 sapling-renderdag = { workspace = true }
 test-case = { workspace = true }
-testutils = { workspace = true }
 tokio = { workspace = true, features = ["full"] }
 
 [features]

lib/tests/Cargo.toml

@@ -0,0 +1,42 @@
+[package]
+name = "jj-lib-tests"
+description = "Integration tests for the jj-lib crate"
+autotests = false
+publish = false
+
+version = { workspace = true }
+edition = { workspace = true }
+rust-version = { workspace = true }
+license = { workspace = true }
+homepage = { workspace = true }
+repository = { workspace = true }
+documentation = { workspace = true }
+readme = { workspace = true }
+
+[[test]]
+name = "runner"
+path = "runner.rs"
+
+[dev-dependencies]
+assert_matches = { workspace = true }
+chrono = { workspace = true }
+config = { workspace = true }
+futures = { workspace = true }
+git2 = { workspace = true }
+gix = { workspace = true }
+hex = { workspace = true }
+indoc = { workspace = true }
+insta = { workspace = true }
+itertools = { workspace = true }
+jj-lib = { workspace = true, features = ["testing"] }
+maplit = { workspace = true }
+num_cpus = { workspace = true }
+pollster = { workspace = true }
+pretty_assertions = { workspace = true }
+rand = { workspace = true }
+tempfile = { workspace = true }
+test-case = { workspace = true }
+testutils = { workspace = true }
+
+[lints]
+workspace = true

lib/tests/runner.rs

@@ -1,9 +1,9 @@
-use std::path::PathBuf;
+use std::path::Path;
 
 #[test]
 fn test_no_forgotten_test_files() {
-    let test_dir = PathBuf::from(env!("CARGO_MANIFEST_DIR")).join("tests");
-    testutils::assert_no_forgotten_test_files(&test_dir);
+    let test_dir = Path::new(env!("CARGO_MANIFEST_DIR"));
+    testutils::assert_no_forgotten_test_files(test_dir);
 }
 
 mod test_annotate;