4 min read

Why Your Coding Tests Won’t Work, and How to Fix Them

joseph cole

Updated on May 2, 2023

Why Your Coding Tests Won’t Work, and How to Fix Them

joseph cole

Updated on May 2, 2023

In this post

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Most coding tests for hiring fail because they measure how well a candidate memorized algorithm puzzles, not how well they build software. They also run too long and in unfamiliar environments. Tests that work use real tasks, take 45 to 60 minutes, allow normal resources and look like the job. Coding Simulations are built around that idea.

Technical hiring still needs coding tests. Resumes alone are unreliable, and interviews favor confident talkers. The problem is not testing. It is what most tests choose to measure.

Why coding tests are worth doing

Done well, coding tests give hiring teams three things interviews cannot:

  • Evidence of skill. A completed task shows how a candidate solves problems, not how they describe solving them.
  • Fair comparison. Everyone works on the same task, so the shortlist rests on comparable results.
  • Less bias in early screening. Structured scoring reduces the weight of pedigree, school name and interview polish.

Skill tests do not answer every question. David Galownia, CEO of Slingshot, made the point that a candidate can ace an assessment and still not fit the team. Testing narrows the field. Interviews and team conversations still decide the hire.

Why most coding tests don’t work

They test memorization, not capability

Algorithm puzzles reward candidates who practiced on puzzle sites. Many strong engineers spend their days designing APIs, debugging production issues and reading other people’s code. A test that asks for an obscure sorting algorithm under a timer screens out people who would do the job well.

They take too long

Multi hour take home projects ask candidates to work unpaid, often on a weekend. Experienced engineers with options skip them. Completion rates drop, and the people who finish are not always the people you most wanted.

They run in unfamiliar conditions

Coding in a bare text box, with no autocomplete, no documentation and no way to run tests, is not how anyone works. Candidates who would perform well in a normal setup look worse than they are.

They ignore how developers work now

Engineers use documentation, search and increasingly AI coding assistants. A test that bans every resource measures something other than the job. A test that allows everything without tracking how it was used measures nothing.

What a good coding test looks like

Weak coding testStrong coding test
Algorithm puzzle unrelated to the roleTask drawn from the actual job
Two to eight hours45 to 60 minutes
Bare editor, no resourcesFamiliar IDE, documentation allowed
Scored only on pass or failScored on correctness, code quality and approach
Same test for every roleMatched to frontend, backend, data, QA or DevOps work
No integrity controlsProctoring and plagiarism checks

A checklist for your next coding assessment:

  1. Base the task on work the person will actually do.
  2. Keep it to 45 to 60 minutes.
  3. Let candidates use the language and tools they know.
  4. Allow documentation, and decide your policy on AI assistants up front.
  5. Score how candidates approach the problem, not only the final output.
  6. Tell candidates what you are evaluating before they start.
  7. Use proctoring to protect test integrity without surprising candidates.
  8. Follow up with a conversation about the code they wrote.

As Daniel Alcanja put it in the original article, “It’s very important to watch how [a developer] codes, and how [a developer] is thinking about the problem.” The follow up conversation is where that happens.

Coding test formats compared

  • Online coding test: quick, scalable first screen for fundamentals.
  • Coding simulation: a realistic project in a full environment; best evidence of job readiness.
  • Live coding interview: shows reasoning and collaboration in real time; costs interviewer time, so use it for finalists.
  • Take home project: flexible but long, and hard to verify who did the work.

Most teams get the best results combining a short simulation for screening with a live coding interview for the final round.

How Glider AI helps you fix your coding tests

Glider AI Coding Simulations replicate a real working environment. In the WebIDE, candidates run complete projects, and the platform auto evaluates frontend, backend or full stack skills on the stack you choose. A virtual desktop option gives candidates a simulated Linux machine. Role based tasks cover data science, frontend, backend, QA and DevOps work, such as building a FIFO cache or implementing paginated REST endpoints.

For broader screening, Technical Assessments cover 250+ languages and technologies with auto scoring and shareable skill reports, and AI Proctoring helps deter plagiarism and proxy test takers. For role specific questions to pair with your tests, browse the Glider AI interview questions library.

Frequently asked questions

Why do coding tests fail to predict job performance?

Many coding tests measure memorized algorithms under artificial conditions instead of the work the role involves. When the task does not resemble the job, the score does not predict how the person will perform on it.

How long should a coding test be?

About 45 to 60 minutes is a good target for a screening test. Longer tests lower completion rates, especially among experienced engineers who have other options.

Should candidates be allowed to use AI tools in coding tests?

Decide your policy before you test and tell candidates. If engineers use AI assistants on the job, allowing them with tracking can produce a more realistic picture than a strict ban.

What is the difference between a coding test and a coding simulation?

A coding test usually presents short, isolated problems. A coding simulation gives candidates a realistic project in a full environment, which shows how they structure, debug and deliver working code.

How do you prevent cheating on coding tests?

Use proctoring, plagiarism checks and unique question sets, and follow up with a live conversation about the submitted code. Candidates who did the work can explain it.

Can you skip coding tests and rely on interviews?

It is risky. Resumes and interviews are weak evidence of coding skill on their own. A short, realistic test gives hiring managers comparable evidence before they invest interview time.

Build coding tests that look like the job

If strong engineers keep failing your test, or weak ones keep passing, the test is the problem. Replace puzzles with realistic work using Glider AI Coding Simulations, and give your hiring managers evidence of how candidates actually build software.

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