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52 lines
1.6 KiB
Markdown
52 lines
1.6 KiB
Markdown
# Kata 15: The Go Test Harness (Subtests, Parallel, Fuzz)
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**Target Idioms:** Table-Driven Tests, `t.Run`, `t.Parallel`, Fuzzing (`go test -fuzz`)
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**Difficulty:** 🟡 Intermediate
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## 🧠 The "Why"
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Developers often write:
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- one-off tests with repetition,
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- unsafe parallel subtests (loop variable capture),
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- no fuzz testing for parsers/sanitizers.
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Idiomatic Go testing is:
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- table-driven,
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- readable failures,
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- parallel where safe,
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- fuzzed for edge cases.
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## 🎯 The Scenario
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You’re implementing a sanitizer:
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- `func NormalizeHeaderKey(s string) (string, error)`
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Rules:
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- only ASCII letters/digits/hyphen allowed
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- normalize to canonical header form (e.g., `content-type` -> `Content-Type`)
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- reject invalid input
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## 🛠 The Challenge
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Write:
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1) The implementation, and
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2) A test suite that proves it’s solid.
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### 1. Functional Requirements
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- [ ] Canonicalize valid inputs.
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- [ ] Reject invalid characters.
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- [ ] Stable behavior (same input => same output).
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### 2. The "Idiomatic" Constraints (Pass/Fail Criteria)
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- [ ] Tests must be **table-driven** with `t.Run`.
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- [ ] Use **parallel subtests** correctly (no loop var capture bugs).
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- [ ] Include a **fuzz test** that:
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- never panics,
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- never returns a string containing invalid characters,
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- roundtrips canonical form (calling Normalize twice is idempotent).
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## 🧪 Self-Correction (Test Yourself)
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- **If parallel subtests flake:** you likely captured the loop variable.
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- **If fuzzing finds panics:** you missed an edge case.
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## 📚 Resources
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- https://go.dev/blog/subtests
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- https://go.dev/wiki/TableDrivenTests
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- https://go.dev/doc/security/fuzz/
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- https://go.dev/doc/tutorial/fuzz
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