End-of-Line Trim
Level: Beginner 15–30 minConcepts: StringsAlgorithms
Solutions: C# | TypeScript | Python
When editing text files often times one ends up putting extra spaces and tabs at the end of each line. Develop a simple algorithm to remove these extra characters. It shall take an input string and produce a right-trimmed output string.
Examples
| Input | Output |
|---|---|
| ”abc" | "abc" |
| "abc " | "abc" |
| "abc\t" | "abc" |
| " abc" | " abc” (does not remove beginning whitespace) |
| “ab\r\n cd \r\n" | "ab\r\ncd\r\n” (removes whitespace at end of second line) |
| “\r\n" | "\r\n” |
Hint
Be sure to handle both Windows \r\n and Unix line endings \n
Reference Walkthrough
Reference implementations in C#, TypeScript, and Python live at tddbuddy-reference-katas/end-of-line-trim. This is an F1 kata — ten scenarios covering CRLF, LF, mixed line endings, whitespace-only lines, leading-whitespace preservation, and empty input — shared across all three languages, each a single pure function trim(input).
- C# (.NET 8, xUnit, FluentAssertions 6.12.0) — walkthrough
- TypeScript (Node 20, Vitest 1.6, TS 5 strict) — walkthrough
- Python (3.11, pytest) — walkthrough
This kata ships in Agent Full-Bake mode at high gear: the rules land as one commit per language, with a brief walkthrough noting there are no builders because the inputs and outputs are the domain. A single left-to-right scan preserves each line’s original terminator (\r\n or \n) byte-for-byte while dropping its trailing space/tab run; a lone \r is treated as content, matching the TDD Buddy spec’s explicit Windows-and-Unix scope. See the repo’s Gears section for when high gear is the right call.
Related reading
- Katas Are Rehearsal, Not Performance
You don't practice TDD on production code. You practice on katas and bring the muscle memory to production. The gap between knowing TDD and doing TDD is reps. - Test Deletion Is a Privileged Operation
The cheapest way for an agent to make a failing test pass is to delete it. That is logical for the agent and catastrophic for the codebase. Tests are append-only by default. Deletion needs a human author, a separate commit, and a separate review. - Refactor Was Always Where Compounding Lived
Red and green were the visible two thirds of TDD. Refactor was the optional polish. Codebases that compound did the refactor pass; codebases that accrete did not. Agents skip refactor by default because it has no green-bar reward, and a year of skipped refactors is how a codebase loses its shape.