test: verify how build-std flag be deserialized now

It doesn't parse as comma-separated list.
It did before #14899

Author: weihanglo

tests/testsuite/config.rs

@@ -2163,3 +2163,65 @@ gitoxide = \"fetch\"
         unstable_flags.gitoxide == expect
     }
 }
+
+#[cargo_test]
+fn build_std() {
+    let gctx = GlobalContextBuilder::new()
+        .env("CARGO_UNSTABLE_BUILD_STD", "core,std,panic_abort")
+        .build();
+    let value = gctx
+        .get::<Option<cargo::core::CliUnstable>>("unstable")
+        .unwrap()
+        .unwrap()
+        .build_std
+        .unwrap();
+    assert_eq!(value, vec!["core,std,panic_abort".to_string()]);
+
+    let gctx = GlobalContextBuilder::new()
+        .config_arg("unstable.build-std=['core', 'std,panic_abort']")
+        .build();
+    let value = gctx
+        .get::<Option<cargo::core::CliUnstable>>("unstable")
+        .unwrap()
+        .unwrap()
+        .build_std
+        .unwrap();
+    assert_eq!(
+        value,
+        vec!["core".to_string(), "std,panic_abort".to_string()]
+    );
+
+    let gctx = GlobalContextBuilder::new()
+        .env(
+            "CARGO_UNSTABLE_BUILD_STD_FEATURES",
+            "backtrace,panic-unwind,windows_raw_dylib",
+        )
+        .build();
+    let value = gctx
+        .get::<Option<cargo::core::CliUnstable>>("unstable")
+        .unwrap()
+        .unwrap()
+        .build_std_features
+        .unwrap();
+    assert_eq!(
+        value,
+        vec!["backtrace,panic-unwind,windows_raw_dylib".to_string()]
+    );
+
+    let gctx = GlobalContextBuilder::new()
+        .config_arg("unstable.build-std-features=['backtrace', 'panic-unwind,windows_raw_dylib']")
+        .build();
+    let value = gctx
+        .get::<Option<cargo::core::CliUnstable>>("unstable")
+        .unwrap()
+        .unwrap()
+        .build_std_features
+        .unwrap();
+    assert_eq!(
+        value,
+        vec![
+            "backtrace".to_string(),
+            "panic-unwind,windows_raw_dylib".to_string()
+        ]
+    );
+}