rust: try to work around windows permission problem during testing

rust/tests/model.rs

@@ -1,5 +1,5 @@
 mod common;
-use std::{f64::consts::PI, ffi::CString, fs::remove_file};
+use std::{f64::consts::PI, ffi::CString, fs};
 
 use common::{get_model, model_dir};
 
@@ -47,11 +47,16 @@ fn logp_gradient() {
 fn model_compiling() {
     let name = "stdnormal";
     let mut base = model_dir();
+    let stan_path_orig = base.join(name).join(format!("{}.stan", name));
+
+    let name = "stdnormal_compile_test";
     base.push(name);
-    let lib_path = base.join(format!("{}_model.so", name));
+    fs::create_dir_all(base.as_path()).unwrap();
     let stan_path = base.join(format!("{}.stan", name));
-    remove_file(lib_path).unwrap();
-    compile_model(stan_path, vec![], vec![], None).unwrap();
+    fs::copy(stan_path_orig, stan_path.as_path()).unwrap();
+
+    let lib_path = base.join(format!("{}_model.so", name));
+    compile_model(stan_path.as_path(), vec![], vec![], None).unwrap();
 
     let (lib, data) = get_model(name);
     let model = Model::new(&lib, data, 42).unwrap();
@@ -62,6 +67,10 @@ fn model_compiling() {
         .unwrap();
     assert_ulps_eq!(logp, (2. * PI).sqrt().recip().ln() - 0.5);
     assert_ulps_eq!(grad[0], -1f64);
+
+    fs::remove_file(lib_path).unwrap_or_default();
+    fs::remove_file(stan_path).unwrap_or_default();
+    fs::remove_dir(base).unwrap_or_default();
 }
 
 #[test]