Debugging a Failing Test Entirely from the Terminal with GitHub Copilot CLI

Manoj Kiran — Sat, 31 Jan 2026 04:10:01 +0000

This is a submission for the GitHub Copilot CLI Challenge

What I Built

I built DevFlow, a minimal TypeScript + Node.js project designed to demonstrate a terminal-first debugging workflow using GitHub Copilot CLI.

The project intentionally includes a failing unit test. Using natural language prompts in the terminal, I asked Copilot CLI to diagnose the failure, explain the root cause, apply a precise fix, and verify the solution — all without opening an editor.

The goal of this project is not application complexity, but to showcase how GitHub Copilot CLI accelerates real debugging workflows directly from the command line.

Repository

Demo Pull Request

Team

@manoj_kiran_4ff6ecaa902bd (submission author)

@kondam_aishwarya_6e02608e (teammate)

Demo

Below is the full terminal-based demo showing how GitHub Copilot CLI was used end-to-end: from detecting a failing test to fixing it and validating the result.

Initial execution of npm test in Windows PowerShell showing a failing unit test. The test sum function adds two numbers fails because the expected value is incorrectly set to 5 while the actual result is 4. This failure is intentional and serves as the starting point for the Copilot CLI debugging demo.

GitHub Copilot CLI launched inside Windows PowerShell using the copilot command. Copilot initializes and requests folder trust before interacting with the project files.

A natural-language prompt is issued to Copilot CLI: “diagnose why npm test is failing”. Copilot begins inspecting the project configuration and test files to understand the failure.

Copilot CLI analyzes the test files and clearly identifies the root cause: the test in tests/failing.test.ts expects sum(2, 2) to equal 5, which is logically incorrect. Copilot explains the issue in plain English before suggesting a fix.

Copilot CLI applies a minimal and precise edit to the codebase, changing the expected value in the failing test from 5 to 4. The terminal output shows the exact file modified and the line change, making the fix fully transparent.

Despite an environment limitation (PowerShell 6+ not installed), Copilot CLI successfully completes the analysis and fix. This demonstrates Copilot CLI’s resilience and usefulness even in constrained environments.

Re-running npm test after Copilot’s fix shows all tests passing successfully. This confirms that the Copilot-generated change resolved the issue correctly and the project is now in a healthy state.

My Experience with GitHub Copilot CLI

Using GitHub Copilot CLI felt like having a debugging partner directly inside the terminal.
Instead of manually scanning test files and logs, I simply described the problem in natural language. Copilot CLI quickly located the issue, explained the reasoning behind the failure, and applied a safe, minimal fix.
What stood out most:

Natural-language debugging without leaving the terminal
Clear explanations, not just code changes
Minimal, auditable edits ideal for PRs and reviews
Terminal-first workflow that fits real developer habits

I used GitHub Copilot CLI to diagnose, fix, and verify a failing test entirely from the terminal using natural language.

This experience showed how GitHub Copilot CLI can significantly reduce debugging time while keeping developers in control.

Forem: Manoj Kiran

Debugging a Failing Test Entirely from the Terminal with GitHub Copilot CLI