Cache config as a file

wasmtime-environ/tests/cache_write_default_config.rs

@@ -0,0 +1,12 @@
+use tempfile;
+use wasmtime_environ::cache_config;
+
+#[test]
+fn test_cache_write_default_config() {
+    let dir = tempfile::tempdir().expect("Can't create temporary directory");
+    let config_path = dir.path().join("cache-config.toml");
+
+    let errors = cache_config::init(true, Some(&config_path), true);
+    assert!(errors.is_empty());
+    assert!(config_path.exists());
+}