Can not run multiple tests in a file

I'm building a GraphQL API and I want to test some resolvers and the database with jest.

Here is my helper file, where I set up the context and the Prisma Client for testing.

import { PrismaClient } from "@prisma/client";
import { ServerInfo } from "apollo-server";
import { execSync } from "child_process";
import getPort, { makeRange } from "get-port";
import { GraphQLClient } from "graphql-request";
import { nanoid } from "nanoid";
import { join } from "path";
import { Client } from "pg";
import { server } from "../api/server";

type TestContext = {
  client: GraphQLClient;
  db: PrismaClient;
};

export function createTestContext(): TestContext {
  let ctx = {} as TestContext;
  const graphqlCtx = graphqlTestContext();
  const prismaCtx = prismaTestContext();

  beforeEach(async () => {
    const client = await graphqlCtx.before();
    const db = await prismaCtx.before();

    Object.assign(ctx, {
      client,
      db,
    });
  });

  afterEach(async () => {
    await graphqlCtx.after();
    await prismaCtx.after();
  });

  return ctx;
}

function graphqlTestContext() {
  let serverInstance: ServerInfo | null = null;

  return {
    async before() {
      const port = await getPort({ port: makeRange(4000, 6000) });
      serverInstance = await server.listen({ port });

      return new GraphQLClient(`http://localhost:${port}`);
    },
    async after() {
      serverInstance?.server.close();
    },
  };
}

function prismaTestContext() {
  const prismaBinary = join(__dirname, "..", "node_modules", ".bin", "prisma");
  let schema = "";
  let databaseUrl = "";
  let prismaClient: null | PrismaClient = null;

  return {
    async before() {
      schema = `test_${nanoid()}`;
      databaseUrl = `postgresql://user:123@localhost:5432/testing?schema=${schema}`;

      process.env.DATABASE_URL = databaseUrl;

      execSync(`${prismaBinary} migrate up --create-db --experimental`, {
        env: {
          ...process.env,
          DATABASE_URL: databaseUrl,
        },
      });

      prismaClient = new PrismaClient();

      return prismaClient;
    },
    async after() {
      const client = new Client({
        connectionString: databaseUrl,
      });
      await client.connect();
      await client.query(`DROP SCHEMA IF EXISTS "${schema}" CASCADE`);
      await client.end();

      await prismaClient?.$disconnect();
    },
  };
}

My test file looks like this:

import { createTestContext } from "./__helpers";

const ctx = createTestContext();

it("register user", async () => {
  const testUser = {
    username: "Test",
    email: "test@test.com",
    password: "password",
  };
  const registerResult = await ctx.client.request(
    `
    mutation registerNewUser($username: String!, $email: String!, $password: String!) {
      register(username: $username, email: $email, password: $password) {
        user {
          user_id
          username
          email
        }
      }
    }
  `,
    {
      username: testUser.username,
      email: testUser.email,
      password: testUser.password,
    }
  );

  const resultUsername = registerResult.register.user.username;
  const resultEmail = registerResult.register.user.email;
  const resultUserID = registerResult.register.user.user_id;

  expect(resultUsername).toBe(testUser.username);
  expect(resultEmail).toBe(testUser.email);
  expect(resultUserID).not.toBeNull;

  const users = await ctx.db.user.findMany();
  const savedUser = users[0];

  expect(savedUser.username).toBe(testUser.username);
  expect(savedUser.email).toBe(testUser.email);
  expect(savedUser.user_id).toBe(resultUserID);
  expect(savedUser.first_name).toBeNull;
  expect(savedUser.last_name).toBeNull;
  expect(savedUser.role).toBe("USER");
  expect(savedUser.password).not.toBe(testUser.password);
});

it("all events", async () => {
  const eventsResult = await ctx.client.request(
    `
    query {
      allEvents {
        event_id
        title
        description
      }
    }
    `
  );

  expect(eventsResult.allEvents.length).toBe(0)
});

When I just run one file with one test in it, everything works. But when I run multiple tests in one file, the first one runs normal, but the ones after not. I receive this error:

The table `test_LjrcmbMjI4vLaDYM9-lvw.Event` does not exist in the current database.: {"response":{"errors":[{"message":"\nInvalid `prisma.event.findMany()` invocation:\n\n\n  The table `test_LjrcmbMjI4vLaDYM9-lvw.Event` does not exist in the current database.","locations":[{"line":3,"column":7}],"path":["allEvents"],"extensions":{"code":"INTERNAL_SERVER_ERROR","exception":{"code":"P2021","clientVersion":"2.11.0","meta":{"table":"test_LjrcmbMjI4vLaDYM9-lvw.Event"}}}}],"data":null,"status":200},"request":{"query":"\n    query {\n      allEvents {\n        event_id\n        title\n        description\n      }\n    }\n    "}}

Also when I run two tests in separated files, on every second test run I get this error:
listen EADDRINUSE: address already in use :::4200

I did the nexus tutorial (Step 4, and 5), where they explained how to test, but somehow it doesn't work. So please help me.

https://nexusjs.org/docs/getting-started/tutorial