test: improve Dockerfile for test environment setup

Co-Authored-By: Nico Krause <[email protected]>

docker/Dockerfile

@@ -1,8 +1,19 @@
 FROM node:20
 WORKDIR /usr/src/app
+
+# Copy package files first
+COPY relay/package*.json ./
+RUN npm install
+
+# Copy remaining files
 COPY relay/ ./
 COPY docker/entrypoint.sh ./
 COPY relay/.env.example ./.env
-RUN rm -rf node_modules && npm install
+
+# Set test environment variables
+ENV CI=true
+ENV RELAY_LOCAL_REGTTEST=true
+ENV NODE_ENV=test
+
 ENTRYPOINT [ "./entrypoint.sh" ]
 CMD [ "node", "src/relay.js"]