fix: always use free port for ZMQ tests

package.json

@@ -23,7 +23,6 @@
     "test:int:watch": "jest test/integration --runInBand --watch",
     "changelog": "conventional-changelog -p angular -i CHANGELOG.md -s",
     "prepublishOnly": "npm run compile",
-
     "python:install": "pip install -r tools/requirements.txt",
     "python:lint": "pylint tools/*.py docker/*.py"
   },
@@ -91,6 +90,7 @@
     "@types/zeromq": "^4.6.2",
     "concurrently": "^4.1.2",
     "conventional-changelog": "^3.1.10",
+    "get-port": "^5.0.0",
     "grpc-tools": "^1.8.0",
     "grpc_tools_node_protoc_ts": "^2.5.4",
     "jest": "^24.9.0",

test/unit/chain/ZmqClient.spec.ts

@@ -1,3 +1,4 @@
+import getPort from 'get-port';
 import zmq, { Socket } from 'zeromq';
 import { randomBytes } from 'crypto';
 import { OutputType } from 'boltz-core';
@@ -37,10 +38,10 @@ describe('ZmqClient', () => {
   const chainClient = new FakedChainClient();
 
   // ZMQ publisher
-  const rawTx = new ZmqPublisher(3000, filters.rawTx);
+  let rawTx: ZmqPublisher;
 
-  const rawBlock = new ZmqPublisher(3001, filters.rawBlock);
-  const hashBlock = new ZmqPublisher(3002, filters.hashBlock);
+  let rawBlock: ZmqPublisher;
+  let hashBlock: ZmqPublisher;
 
   const sendHashBlock = (height?: number, orphan = false) => {
     const { hash } = chainClient.generateBlock(height, orphan);
@@ -75,6 +76,13 @@ describe('ZmqClient', () => {
     chainClient.getRawTransactionVerbose,
   );
 
+  beforeAll(async () => {
+    rawTx = new ZmqPublisher(await getPort(), filters.rawTx);
+
+    rawBlock = new ZmqPublisher(await getPort(), filters.rawBlock);
+    hashBlock = new ZmqPublisher(await getPort(), filters.hashBlock);
+  });
+
   test('should not init without needed subscriptions', async () => {
     const rejectZmqClient = new ZmqClient(
       'BTC',