feat: eval_state::test_init

(cherry picked from commit 040982222c9eb8ea91d7174e6f2e21bbc6cda8a4)

rust/nix-expr/src/eval_state.rs

@@ -353,27 +353,32 @@ impl Drop for EvalState {
     }
 }
 
+/// Initialize the Nix library for testing. This includes some modifications to the Nix settings, that must not be used in production.
+/// Use at your own peril, in rust test suites.
+pub fn test_init() {
+    init().unwrap();
+
+    // During development, we encountered a problem where the build hook
+    // would cause the test suite to reinvokes itself, causing an infinite loop.
+    // While _NIX_TEST_NO_SANDBOX=1 should prevent this, we may also set the
+    // build hook to "" to prevent this.
+    // settings::set("build-hook", "")?;
+
+    // When testing in the sandbox, the default build dir would be a parent of the storeDir,
+    // which causes an error. So we set a custom build dir here.
+    nix_util::settings::set("sandbox-build-dir", "/custom-build-dir-for-test").unwrap();
+    std::env::set_var("_NIX_TEST_NO_SANDBOX", "1");
+}
+
 #[cfg(test)]
 mod tests {
     use ctor::ctor;
-    use nix_util::settings;
 
     use super::*;
 
     #[ctor]
     fn setup() {
-        init().unwrap();
+        test_init();
-
-        // During development, we encountered a problem where the build hook
-        // would cause the test suite to reinvokes itself, causing an infinite loop.
-        // While _NIX_TEST_NO_SANDBOX=1 should prevent this, we may also set the
-        // build hook to "" to prevent this.
-        // settings::set("build-hook", "")?;
-
-        // When testing in the sandbox, the default build dir would be a parent of the storeDir,
-        // which causes an error. So we set a custom build dir here.
-        settings::set("sandbox-build-dir", "/custom-build-dir-for-test").unwrap();
-        std::env::set_var("_NIX_TEST_NO_SANDBOX", "1");
     }
 
     #[test]