test: lockfile path unstable feature tests

tests/testsuite/lockfile_path.rs

@@ -10,6 +10,50 @@ use cargo_test_support::{
     basic_bin_manifest, cargo_test, project, symlink_supported, ProjectBuilder,
 };
 
+///////////////////////////////
+//// Unstable feature tests start
+///////////////////////////////
+
+#[cargo_test]
+fn must_have_unstable_options() {
+    let lockfile_path = "mylockfile/is/burried/Cargo.lock";
+    let p = make_project().build();
+
+    p.cargo("generate-lockfile")
+        .masquerade_as_nightly_cargo(&["lockfile-path"])
+        .arg("--lockfile-path")
+        .arg(lockfile_path)
+        .with_stderr_data(str![[
+            r#"[ERROR] the `--lockfile-path` flag is unstable, pass `-Z unstable-options` to enable it
+See https://github.com/rust-lang/cargo/issues/5707 for more information about the `--lockfile-path` flag.
+
+"#]])
+        .with_status(101)
+        .run();
+}
+
+#[cargo_test]
+fn must_be_nightly() {
+    let lockfile_path = "mylockfile/is/burried/Cargo.lock";
+    let p = make_project().build();
+
+    p.cargo("generate-lockfile")
+        .arg("-Zunstable-options")
+        .arg("--lockfile-path")
+        .arg(lockfile_path)
+        .with_stderr_data(str![[
+            r#"[ERROR] the `-Z` flag is only accepted on the nightly channel of Cargo, but this is the `stable` channel
+See https://doc.rust-lang.org/book/appendix-07-nightly-rust.html for more information about Rust release channels.
+
+"#]])
+        .with_status(101)
+        .run();
+}
+
+///////////////////////////////
+//// Unstable feature tests end
+///////////////////////////////
+
 #[cargo_test]
 fn basic_lockfile_created() {
     let lockfile_path = "mylockfile/is/burried/Cargo.lock";