Tests for cache system

wasmtime-environ/tests/cache_fail_usage_without_init.rs

@@ -0,0 +1,7 @@
+use wasmtime_environ::cache_conf;
+
+#[test]
+#[should_panic]
+fn test_fail_usage_without_init() {
+    let _ = cache_conf::cache_directory();
+}