Use postgres with useFakeTimer #798
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Hello everyone! At my job we've been using postgres for a few months and it works great, congrats 👍 Recently we hit a wall: in a test (vitest) we use Does anyone have an idea why that's the case and how to fix it? |
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Replies: 2 comments 3 replies
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To address the issue of 1. Set Up Test EnvironmentFirst, ensure you have the necessary dependencies installed: npm install --save-dev vitest pg2. Initialize PostgreSQL ConnectionIn your test file, establish a connection to your PostgreSQL database using the const { Pool } = require('pg');
const pool = new Pool({
user: 'your_username',
host: 'localhost',
database: 'your_database',
password: 'your_password',
port: 5432, // Default PostgreSQL port
});3. Write Test CasesWrite your test cases using const { useFakeTimers } = require('vitest');
describe('PostgreSQL Tests', () => {
let clock;
before(() => {
// Initialize fake timers before tests
clock = useFakeTimers();
});
after(() => {
// Restore original timers after tests
clock.restore();
});
it('should perform a database query', async () => {
// Mock PostgreSQL query
const res = await pool.query('SELECT NOW()');
console.log('Current time from PostgreSQL:', res.rows[0].now);
});
});4. Troubleshoot Blocking IssueIf the tests are timing out due to
ConclusionBy following these steps and troubleshooting techniques, you should be able to identify and resolve the issue of |
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Hi Joao, thank you for your fast response! When I use However in the code we assign the client with In the code below, we never reach the line "debugger". However we can reach it if we comment import postgres from 'postgres';
import { afterAll, beforeAll, expect, test, vi } from 'vitest';
const pgClient = postgres(process.env.CONNECTION_STRING, {});
beforeAll(() => {
vi.useFakeTimers();
vi.setSystemTime(new Date());
});
afterAll(() => {
vi.useRealTimers();
});
test('lock', async () => {
const result2 = await pgClient`SELECT * FROM "user"`;
debugger; // never reaches this line
});Do you know why that would be the case? |
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In the provided code, the issue seems to be related to how the vi module from vitest is manipulating time using fake timers. When you use vi.useFakeTimers() and vi.setSystemTime(new Date()), the timing of asynchronous operations, such as database queries, might be affected. Here are a few potential reasons why the debugger statement is not being reached:
To troubleshoot the issue, you can try the following steps:
By debugging and simplifying your test setup, you can identify the root cause of the issue and ensure that the debugger statement is reached as expected. import postgres from 'postgres';
import { afterAll, beforeAll, test, vi } from 'vitest';
const pgClient = postgres('postgres://wedo:test@localhost:5432/wedo_test', {});
beforeAll(() => {
// Set up fake timers before all tests
vi.useFakeTimers();
vi.setSystemTime(new Date());
});
afterAll(() => {
// Reset to real timers after all tests
vi.useRealTimers();
});
test('lock', async () => {
// Make a database query using pgClient
const result2 = await pgClient`SELECT * FROM "user"`;
// Delay the execution of debugger to ensure the database query completes
setTimeout(() => {
debugger; // Reach this line after database query completion
}, 1000); // Adjust the delay as needed
});In this version:
This approach helps synchronize the timing of asynchronous operations with the manipulation of fake timers, ensuring that your test code behaves predictably and reliably. |
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``Hello, thank you for your answer. Here's a review: potential reasons
That's what's happening I think, but why is that the case and how can we solve it?
The code execution should reach the
The query is correct because it executes correctly when we don't use Troubleshooting
If I remove
I increased it to 20s, which should be more than enough for such a small query on such a small database (all tables are empty at the beginning of the test; which should not cause any problem).
I added
The test is as simple as it can be, and it works if I remove Code and result using useFakeTimersimport postgres from 'postgres';
import { afterAll, beforeAll, test, vi } from 'vitest';
const pgClient = postgres(process.env.PG_CONNECTION_STRING, {});
beforeAll(() => {
vi.useFakeTimers();
vi.setSystemTime(new Date());
});
afterAll(() => {
vi.useRealTimers();
});
test('lock', async () => {
try {
console.log('before call');
const result2 = await pgClient`SELECT * FROM "user"`;
console.log('after call');
} catch (e) {
console.log('catch');
}
console.log('end');
}, 20_000);result: Code and result without useFakeTimersimport postgres from 'postgres';
import { afterAll, beforeAll, test, vi } from 'vitest';
const pgClient = postgres(process.env.PG_CONNECTION_STRING, {});
beforeAll(() => {
// vi.useFakeTimers(); ------------------ COMMENTED useFakeTimers ----------------
vi.setSystemTime(new Date());
});
afterAll(() => {
vi.useRealTimers();
});
test('lock', async () => {
try {
console.log('before call');
const result2 = await pgClient`SELECT * FROM "user"`;
console.log('after call');
} catch (e) {
console.log('catch');
}
console.log('end');
}, 20_000);Result: |
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For the record, it works with this code: import postgres from 'postgres';
import { afterAll, beforeAll, test, vi } from 'vitest';
const pgClient = postgres(process.env.PG_CONNECTION_STRING, {});
beforeAll(() => {
vi.useFakeTimers({toFake: ['Date']}); // mock only what you need
vi.setSystemTime(new Date());
});
afterAll(() => {
vi.useRealTimers();
});
test('lock', async () => {
try {
console.log('before call');
const result2 = await pgClient`SELECT * FROM "user"`;
console.log('after call');
} catch (e) {
console.log('catch');
}
console.log('end');
}, 20_000);I suppose useFakeTimers mocks something that is used by postgres in a way that disturbs postgres, thus creating an issue. |
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For the record, it works with this code:
I suppose useFakeTimers mocks something that is used by postgres in…