ethereum: partially fix npm run test

ethereum/README.md

@@ -28,7 +28,7 @@ For each test run:
 
 Run `npx ganache-cli --deterministic --time "1970-01-01T00:00:00+00:00"` to start a chain.
 
-Run the tests using `npm test`
+Run the tests using `npm run test`
 
 ### User methods
 

ethereum/package.json

@@ -16,7 +16,7 @@
   },
   "scripts": {
     "build": "truffle compile",
-    "test": "cp node_modules/@openzeppelin/contracts/build/contracts/* build/contracts/ && truffle test"
+    "test": "mkdir -p build/contracts && cp node_modules/@openzeppelin/contracts/build/contracts/* build/contracts/ && truffle test"
   },
   "author": "",
   "license": "ISC",