# Always Check Your Tests Against Faulty Inputs

DevFeed: [Always Check Your Tests Against Faulty Inputs](<https://devfeed.tech/articles/always-check-your-tests-against-faulty-inputs-11218.md>)

Original publisher: [Read original article](<https://blog.ipspace.net/2025/07/tests-should-detect-errors/>)

Published: 2025-07-21T05:19:00Z

Content type: tutorial

Language: en

Sources: [ipSpace.net blog](<https://devfeed.tech/sources/ipspace-net-blog.md>)

Topics: [Testing](<https://devfeed.tech/topics/testing.md>), [Network](<https://devfeed.tech/topics/network.md>)

Tags: [automation](<https://devfeed.tech/tags/automation.md>), [blog](<https://devfeed.tech/tags/blog.md>), [blog-post](<https://devfeed.tech/tags/blog-post.md>), [false-negative](<https://devfeed.tech/tags/false-negative.md>), [false-positive](<https://devfeed.tech/tags/false-positive.md>), [false-positives](<https://devfeed.tech/tags/false-positives.md>), [netlab](<https://devfeed.tech/tags/netlab.md>), [network](<https://devfeed.tech/tags/network.md>), [ospf](<https://devfeed.tech/tags/ospf.md>), [testing](<https://devfeed.tech/tags/testing.md>), [tests](<https://devfeed.tech/tags/tests.md>)

## AI overview

The article explains that tests must be checked with faulty inputs, not only under correct conditions. It uses a netlab integration test for mismatched OSPF network types as an example of a test that could miss the targeted error, and warns that false positives can be more harmful than false negatives.

## Source excerpt

A while ago, I published a blog post proudly describing the netlab integration test that should check for incorrect OSPF network types in netlab-generated device configurations. Almost immediately, Erik Auerswald pointed out that my test wouldn't detect that error (it might detect other errors, though) as the OSPF network adjacency is always established even when the adjacent routers have mismatching OSPF network types. I made one of the oldest testing mistakes: I checked whether my test would work under the correct conditions but not whether it would detect an incorrect condition. Read more ...