How to share an object between multiple test suites in Jest?

Question

I need to share an object (db connection pool) between multiple test suites in Jest.
I have read about globalSetup and it seems to be the right place to initialize this object, but how can I pass that object from globalSetup context to each test suite context?

Answer 1

I'm dealing with a very similar issue, although in my case I was trying to share a single DB container (I'm using dockerode) that I spin up once before all tests and remove after to conserve the overhead of spinning a container for each suite.

Unfortunately for us, after going over a lot of documentation and Github issues my conclusion is that this is by design since Jest's philosophy is to run tests sandboxed and under that restriction, I totally get why they choose not to support this.

Specifically, for my use case I ended up spinning a container in a globalSetup script, tagging it with some unique identifier for the current test run (say, timestamp) and removing it at the end with a globalTeardown (that works since global steps can share state between them).

This looks roughly like:

const options: ContainerCreateOptions = {
Image: POSTGRES_IMAGE,
Tty: false,
HostConfig: {
    AutoRemove: true,
    PortBindings: {'5432/tcp': [{HostPort: `${randomPort}/tcp`}]}
},
Env: [`POSTGRES_DB=${this.env['DB_NAME']}`,
    `POSTGRES_USER=${this.env['DB_USERNAME']}`,
    `POSTGRES_PASSWORD=${this.env['DB_PASSWORD']}`]
};
options.Labels = { testContainer: `${CURRENT_TEST_TIMESTAMP}`};
let container = await this.docker.createContainer(options);
await container.start();

where this.env in my case is a .env file I preload based on the test.

To get the container port/ip (or whatever else I'm interested in) for my tests I use a custom envrironment that my DB-requiring tests use to expose the relevant information on a global variable (reminder: you can only put primitives and objects on global, not instances).

In your case, the requirement to pass a connection pool between suites is probably just not suited for jest since it will never let you pass around an instance between different suites (at least that's my understanding based on all of the links I shared). You can, however, try either:

• Put all tests that need the same connection pool into a single suite/file (not great but would answer your needs)
• Do something similar to what I suggested (setup DB once in global, construct connection pool in custom env and then at least each suite gets its own pool) that way you have a lot of code reuse for setup which is nice. Something similar is discussed here.

Miscalenous: I stumbled across testdeck which might answer your needs as well (setup an abstract test class with your connection pool and inherit it in all required tests) - I didn't try it so I don't know how it will behave with Jest, but when I was writing in Java that's how we used to achieve similar functionality with TestNG