Cache config as a file

wasmtime-environ/tests/cache_fail_invalid_path_to_config.rs

@@ -0,0 +1,10 @@
+use tempfile;
+use wasmtime_environ::cache_config;
+
+#[test]
+fn test_cache_fail_invalid_path_to_config() {
+    let dir = tempfile::tempdir().expect("Can't create temporary directory");
+    let config_path = dir.path().join("cache-config.toml"); // doesn't exist
+    let errors = cache_config::init(true, Some(&config_path), false);
+    assert!(!errors.is_empty());
+}