Testing GET endpoints in Express - Step-by-Step Execution

Concept Flow - Testing GET endpoints

Start Test

↓

Send GET Request

↓

Server Receives Request

↓

Server Processes Request

↓

Server Sends Response

↓

Test Receives Response

↓

Check Status & Body

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Pass or Fail Test

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End Test

The test sends a GET request to the server, waits for the response, then checks if the response status and body match expectations.

Execution Sample

Express

import request from 'supertest';
import app from './app';

test('GET /hello returns 200 and greeting', async () => {
  const res = await request(app).get('/hello');
  expect(res.status).toBe(200);
  expect(res.text).toBe('Hello World!');
});

This test sends a GET request to '/hello' and checks if the response status is 200 and the body text is 'Hello World!'.

Execution Table

Step	Action	Request Sent	Server Response	Test Check	Result
1	Send GET request to /hello	GET /hello	Waiting...	Waiting...	Pending
2	Server receives request	GET /hello	Processing	Waiting...	Pending
3	Server processes and sends response	GET /hello	Status: 200, Body: 'Hello World!'	Waiting...	Pending
4	Test receives response	GET /hello	Status: 200, Body: 'Hello World!'	Check status == 200	Pass
5	Test checks response body	GET /hello	Status: 200, Body: 'Hello World!'	Check body == 'Hello World!'	Pass
6	Test ends	GET /hello	Status: 200, Body: 'Hello World!'	All checks passed	Test Passed

💡 Test ends after all assertions pass confirming GET endpoint works as expected.

Variable Tracker

Variable	Start	After Step 1	After Step 3	After Step 5	Final
res.status	undefined	undefined	200	200	200
res.text	undefined	undefined	'Hello World!'	'Hello World!'	'Hello World!'
testResult	undefined	Pending	Pending	Pass	Test Passed

Key Moments - 3 Insights

Why does the test wait after sending the GET request before checking the response?

Because the server needs time to process the request and send back a response. The test waits for the response before checking status and body, as shown in steps 1 to 4 in the execution_table.

What happens if the response status is not 200?

The test will fail at the status check step (step 4). The test expects 200, so any other status causes a failure, stopping further checks.

Why do we check both status and body in the test?

Checking status ensures the request succeeded, and checking body confirms the server returned the correct content. Both are needed to fully verify the GET endpoint works, as shown in steps 4 and 5.

Visual Quiz - 3 Questions

Look at the execution_table, what is the response status at step 3?

A 500

B 404

C 200

D undefined

💡 Hint

Check the 'Server Response' column at step 3 in the execution_table.

At which step does the test check the response body?

A Step 2

B Step 5

C Step 4

D Step 6

💡 Hint

Look at the 'Test Check' column in the execution_table for the step checking body.

If the server responded with status 404, what would happen in the test?

A Test fails at status check

B Test skips status check

C Test passes anyway

D Test passes but body check fails

💡 Hint

Refer to the key_moments about what happens if status is not 200.

Concept Snapshot

Testing GET endpoints in Express:
- Use a test tool like supertest to send GET requests.
- Await the server response asynchronously.
- Check response status code (e.g., 200).
- Check response body content.
- Pass test only if all checks succeed.

Full Transcript

This visual execution shows how to test GET endpoints in Express using a test framework and supertest. The test sends a GET request to the server, waits for the response, then checks the status code and response body. The execution table traces each step from sending the request, server processing, receiving the response, to checking assertions. Variables like response status and text update as the test progresses. Key moments clarify why waiting for the response is necessary and why both status and body are checked. The quiz questions reinforce understanding by referencing the execution steps and outcomes. This approach helps beginners see exactly how testing GET endpoints works step-by-step.