chore(tests): performance improvements for backend tests

The backend end-to-end tests run with many parallel workers that
each start a full NestJS application including database connection
pools, HTTP server and so on. This can easily result in performance
bottlenecks - which is even the reason why we added the --runInBand
option for the CI. The performance can be improved by constraining
the number of workers and memory allocated per worker in our jest
config. Furthermore, we can forcefully close open HTTP connections
in the test cleanup. This terminates connections with a keepalive
flag, that would persist for a while longer otherwise. The following
`this.app.close()` waits for keepalive requests, so this reduces the
wait time.

Signed-off-by: Erik Michelson <github@erik.michelson.eu>

backend/jest-e2e.json

@@ -19,5 +19,7 @@
   },
   "coverageDirectory": "./coverage-e2e",
   "testTimeout": 15000,
-  "reporters": ["default", "github-actions"]
+  "reporters": ["default", "github-actions"],
+  "maxWorkers": 4,
+  "workerIdleMemoryLimit": "1GB"
 }

backend/test/test-setup.ts

@@ -150,6 +150,7 @@ export class TestSetup {
    * Cleans up Fastify, NestJS, and the database from a test run.
    */
   public async cleanup(): Promise<void> {
+    this.app.getHttpServer().closeAllConnections();
     await this.app.close();
     if (this.knexInstance) {
       await this.knexInstance.destroy();