diff --git a/nix-js/tests/lang.rs b/nix-js/tests/lang.rs
index 313d803..827e6d9 100644
--- a/nix-js/tests/lang.rs
+++ b/nix-js/tests/lang.rs
@@ -37,10 +37,11 @@ fn format_value(value: &Value) -> String {
 }
 
 macro_rules! eval_okay_test {
-    ($(#[$attr:meta])* $name:ident) => {
+    ($(#[$attr:meta])* $name:ident$(, $pre:expr)?) => {
         $(#[$attr])*
         #[test]
         fn $name() {
+            $(($pre)();)?
             let test_name = concat!("eval-okay-", stringify!($name))
                 .replace("_", "-")
                 .replace("r#", "");
@@ -133,7 +134,11 @@ eval_okay_test!(#[ignore = "not implemented: hashString"] hashstring);
 eval_okay_test!(getattrpos);
 eval_okay_test!(getattrpos_functionargs);
 eval_okay_test!(getattrpos_undefined);
-eval_okay_test!(getenv);
+eval_okay_test!(getenv, || {
+    unsafe {
+        std::env::set_var("TEST_VAR", "foo")
+    };
+});
 eval_okay_test!(groupBy);
 eval_okay_test!(r#if);
 eval_okay_test!(ind_string);