There was still one occasional problem while running cargo test, it would fail sometimes. Added a serial preprocessor to ensure the underlying arduino command didn't run pipelined. That fixed the problem

tests/script_execution_test.rs

@@ -19,6 +19,7 @@ use std::fs;
 use std::path::Path;
 use std::process::Command;
 use tempfile::TempDir;
+use serial_test::serial;
 
 use anvil::templates::{TemplateContext, TemplateManager};
 use anvil::version::ANVIL_VERSION;
@@ -511,6 +512,7 @@ fn test_inner_run_tests_idempotent() {
 // ==========================================================================
 
 #[test]
+#[serial]
 fn test_build_script_compiles_sketch() {
     require_build_script_deps();