I am totally new to using Jest, especially in regards to unit tests, and I am struggling to write a test for a specific scenario.
I know that you can mock an external module like this..
jest.mock('@organisation/library', () => ({
Database: jest.fn(() => ({})),
....,
....,
}))
If you want to use an actual method from that module, you can do something like
const database = jest.requireActual('@organisation/library')What I'm trying to do is mock only one method from the library, not the entire library itself.
Is this possible?
Let me explain the code a bit further.
We have a file called StationRepository. This file includes a Database method from our JS framework.
The file then calls the database and returns a value.
I want to test that database query.
Here is the test
import { DatabaseModule, Pg } from '@organisation/framework'
import { StationRepository } from './StationRepository'
import { DatabaseConfig } from '../../spec'
const DatabaseInstance = new DatabaseModule()
beforeAll(async () => {
DatabaseInstance.add('default', new Pg('default', DatabaseConfig))
jest.clearAllMocks()
})
afterAll(async () => {
const database = DatabaseInstance.get()
await database.disconnect()
})
describe('find timezone', () => {
it('can find a timezone', async () => {
const ids = [1, 2]
const expected = ['Pacific/Auckland', 'Australia/Adelaide']
const results = []
for (const id of ids) {
const timezone: string | null = await StationRepository.findTimezone(id)
results.push(timezone)
}
expect(results).toEqual(expected)
})
})
And the method in the repository
import { DatabaseFacade as Database } from '@organisation/framework'
export class StationRepository {
/**
* Find Timezone
*
* Finds the station or system timezone and returns
* will return station timezone
* if no station timezone will return system timezone
* if no system timezone null will be returned
*
* @param {number} stationId - The station id to search on
* @param {string} db - Optional - The Database connection
*
* @return string | null
*/
public static findTimezone = async (
stationId: number,
db?: string,
): Promise<string | null> => {
const query = `
SELECT
(CASE
WHEN stations.timezone IS NOT NULL
THEN stations.timezone
WHEN systems.timezone IS NOT NULL
THEN systems.timezone
END
) AS timezone
FROM
stations
INNER JOIN systems ON systems.id = stations.system_id
WHERE
stations.id = $1
`
const result = await Database.get(db).queryOne<StationTimezone | null>.(
query,
[stationId],
)
if (!result) {
return null
}
return result.timezone
}
}
Everything seems to be working well, setting up the connection from the test and all. However, it fails on the actual query Database.get(). This is being loaded in from the framework. If I mock the entire framework, everything breaks.
So essentially, what I want to do is have the framework run normally, but only replace the DatabaseFacade section to use the DatabaseInstance created in the test.
Is this possible?