fix(go-runner): clear mod cache before running tests

Author: not-matthias

go-runner/src/runner/mod.rs

@@ -8,13 +8,24 @@ use tempfile::TempDir;
 
 mod overlay;
 
-pub fn run_cmd<P: AsRef<Path>>(
+fn run_cmd<P: AsRef<Path>>(
     profile_dir: P,
     dir: P,
     cli: &Cli,
 ) -> anyhow::Result<(TempDir, Command)> {
     let (_dir, overlay_file) = overlay::get_overlay_file(profile_dir.as_ref())?;
 
+    // Clear the mod cache which can cause issues with `-overlay` since it's assumed to
+    // be read-only. Tests can otherwise crash at runtime with this error:
+    // `go: overlay contains a replacement for /home/runner/go/pkg/mod/golang.org/toolchain@v0.0.1-go1.25.0.linux-arm64/src/testing/benchmark.go. Files beneath GOMODCACHE (/home/runner/go/pkg/mod) must not be replaced.
+    //
+    // See: https://github.com/golang/go/issues/71783#issuecomment-2666541103
+    Command::new("go")
+        .arg("clean")
+        .arg("-modcache")
+        .output()
+        .unwrap();
+
     // Execute the `go test` command using the go binary, rather than the one in the PATH
     // to avoid running into infinite loops with the runner which tries to intercept `go test`.
     let go_binary = find_go_binary()?;