How to Fake Pool Connection Using Sinon.js for Unit Testing in Node.js

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The Problem: Testing Database Queries

In a typical scenario, developers often need to write functions that interact with a database. For instance, the following function connects to a PostgreSQL pool and executes queries based on provided parameters:

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Step 1: Setting Up Your Testing Environment

First, ensure you have the following packages installed:

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Step 2: Faking the Pool Connection

To fake the pool connection, we'll use proxyquire along with sinon.

Here’s a detailed breakdown of how to write the test:

Create a mock response:
You will need to define what response should be returned when the fake queries are executed. For instance, you might want to return a simple message:

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Create client and pool stubs:
These will mimic the behavior of the actual database client and pool:

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Stub the Pool constructor:
Replace the actual pg pool with your stub:

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Use proxyquire to load your module:
Ensure it uses the stubs instead of the real Postgres library:

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Step 3: Writing the Test Case

Here’s how the full test could look:

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Step 4: Run Your Tests

After implementing your tests, you can run them to ensure everything functions as expected. When running the test, it should simulate a connection to the database without actually hitting it, returning the mocked response instead.

Conclusion