Cache config as a file

wasmtime-environ/tests/cache_fail_invalid_config.rs

@@ -0,0 +1,23 @@
+use std::fs;
+use tempfile;
+use wasmtime_environ::cache_config;
+
+#[test]
+fn test_cache_fail_invalid_config() {
+    let dir = tempfile::tempdir().expect("Can't create temporary directory");
+    let baseline_compression_level = -4;
+
+    let config_path = dir.path().join("cache-config.toml");
+    let config_content = format!(
+        "[cache]\n\
+         enabled = true\n\
+         directory = {}\n\
+         baseline-compression-level = {}\n",
+        toml::to_string_pretty(&format!("{}", config_path.display())).unwrap(), // directory is a file -- incorrect!
+        baseline_compression_level,
+    );
+    fs::write(&config_path, config_content).expect("Failed to write test config file");
+
+    let errors = cache_config::init(true, Some(&config_path), false);
+    assert!(!errors.is_empty());
+}