feat(test): test the readme copying

tests/readme.rs

@@ -0,0 +1,17 @@
+extern crate wasm_pack;
+
+use std::fs;
+
+use wasm_pack::readme;
+
+#[test]
+fn it_copies_a_readme_default_path() {
+    assert!(readme::copy_from_crate(".").is_ok());
+    assert!(fs::metadata("./pkg/README.md").is_ok());
+}
+
+#[test]
+fn it_creates_a_package_json_provided_path() {
+    assert!(readme::copy_from_crate("./examples/js-hello-world").is_ok());
+    assert!(fs::metadata("./examples/js-hello-world/pkg/README.md").is_ok());
+}