Guides > Agentic Engineering Patterns > Red/green TDD
Changes to Red/green TDD
Feb. 28, 2026, 10:40 p.m.
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Every good model understands "red/green TDD" as a shorthand for the much longer "use test driven development, write the tests first, confirm that the tests fail before you implement the change that gets them to pass".
Example prompt:
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-> Build a Python function to extract headers from a markdown string. Use red/green TDD.
+````markdown-copy
+Build a Python function to extract headers from a markdown string. Use red/green TDD.
+````
Feb. 25, 2026, 11:47 p.m.
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-Red/green TDD!
+Red/green TDD
Feb. 25, 2026, 11:47 p.m.
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-Red/green TDD
+Red/green TDD!
Feb. 25, 2026, 1:19 p.m. (notable)
Remove the examples from ChatGPT and Claude - they weren't good enough illustrations of the concept.
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Example prompt:
-> Build a Python function to extract headers from a markdown string. Use red/green TDD.
-
-Here's what I got [from Claude](https://claude.ai/share/2b9b952a-149b-4864-afb0-46f59b90b458) and [from ChatGPT](https://chatgpt.com/share/699beb6f-adc8-8006-a706-6bbfdcdca538). Normally I would use a coding agent like Claude Code or OpenAI Codex, but this example is simple enough that both Claude and ChatGPT can implement it using their default code environments.
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-(I did have to append "Use your code environment" to the ChatGPT prompt. When I tried without that it wrote the code and tests without actually executing them.)
+> Build a Python function to extract headers from a markdown string. Use red/green TDD.
Feb. 23, 2026, 12:44 p.m.
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Here's what I got [from Claude](https://claude.ai/share/2b9b952a-149b-4864-afb0-46f59b90b458) and [from ChatGPT](https://chatgpt.com/share/699beb6f-adc8-8006-a706-6bbfdcdca538). Normally I would use a coding agent like Claude Code or OpenAI Codex, but this example is simple enough that both Claude and ChatGPT can implement it using their default code environments.
-I did have to append "Use your code environment" to the ChatGPT prompt. When I tried without that it wrote the code and tests without actually executing them.
+(I did have to append "Use your code environment" to the ChatGPT prompt. When I tried without that it wrote the code and tests without actually executing them.)
Feb. 23, 2026, 7:12 a.m.
Initial version.