# zig-testing

A skill that walks the agent through Zig testing: zig build test, filters, comptime checks, the test allocator and the built-in fuzzer.

- skill · `type=skill` · Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, OpenCode · 440 installs · ★ 267
- Author: mohitmishra786
- License: MIT · policy=mirror · the beginning of the file is at the end of this page
- Source: https://github.com/mohitmishra786/low-level-dev-skills/tree/HEAD/skills/zig/zig-testing/SKILL.md
- Updated: 2026-06-27
- HTML: https://affpapa.org/en/nevibecode/skills/zig-testing

## What it does

The skill covers writing and running tests in Zig. Tests sit in the same file as the code, and the agent gets the exact commands: `zig test src/math.zig`, `zig build test`, verbose output with `-- --verbose`, and name filtering through `-- --test-filter "add"`. A separate section handles `build.zig`, including `test` and `test-unit` steps and splitting unit tests from integration tests into separate executables.

Memory gets its own part. `std.testing.allocator` wraps a `GeneralPurposeAllocator` in test mode and reports leaks at the end of each test, which makes `defer list.deinit()` matter. In the manual allocator example the result of `gpa.deinit()` is compared against `.ok`; a `.leak` value fails the test. The assertion set is listed too: `expectEqual`, `expectEqualStrings`, `expectEqualSlices`, `expectApproxEqAbs`, `expectError`.

Comptime tests check constants and type properties during compilation, down to `@alignOf` and `@sizeOf`. The built-in fuzzer arrived in Zig 0.14: entry point `export fn fuzz(input: []const u8)`, run with `zig build fuzz -Dfuzz=fuzz_target`, corpus in `corpus/`, crashes saved as artifacts. Fuzzing needs instrumentation enabled in `build.zig` — skip `fuzz_exe.root_module.fuzz = true` and the step does nothing. The skill installs across six platforms, though the examples assume Zig 0.14 or later.

## Install

### Claude Code (native platform)

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill zig-testing -a claude-code
```

2. **Manually: put the files in place**
- File: `~/.claude/skills/zig-testing/SKILL.md` — Copy the whole skill folder; for one project use .claude/skills/zig-testing/

### Codex

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill zig-testing -a codex
```

2. **Manually: put the files in place**
- File: `.agents/skills/zig-testing/SKILL.md` — For all projects use ~/.agents/skills/

### Cursor

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill zig-testing -a cursor
```

2. **Manually: put the files in place**
- File: `.cursor/skills/zig-testing/SKILL.md` — Cursor also reads .agents/skills/ and .claude/skills/

### GitHub Copilot

1. **GitHub CLI**
```bash
gh skill install mohitmishra786/low-level-dev-skills zig-testing
```

2. **Manually: put the files in place**
- File: `.github/skills/zig-testing/SKILL.md`

### Gemini CLI

1. **Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill zig-testing -a gemini-cli
```

2. **Platform CLI**
```bash
gemini skills install https://github.com/mohitmishra786/low-level-dev-skills --path skills/zig/zig-testing
```

### Windsurf (Devin Desktop)

**Manually: put the files in place**
- File: `.devin/skills/zig-testing/SKILL.md` — The legacy .windsurf/skills/ path still works

### OpenCode

**Skills CLI (Vercel)**
```bash
npx skills add mohitmishra786/low-level-dev-skills --skill zig-testing -a opencode
```

### Claude.ai

**Claude.ai**
- Zip the folder and upload it in Settings → Capabilities → Skills

Where a file is given instead of a command, copy the files from the source to that path: https://github.com/mohitmishra786/low-level-dev-skills/tree/HEAD/skills/zig/zig-testing/SKILL.md

## When to use it
- run every project test with `zig build test`
- narrow a test run to a name substring with `--test-filter`
- catch a memory leak in a test and find the missing `defer`
- verify a type's size and alignment at compile time
- fuzz a parser and keep the crashing input in the corpus

## Example prompts
- write tests for `src/math.zig` and run them with `zig build test`
- add a `test-unit` step to `build.zig` for unit tests only
- set up fuzzing for `parseInput` and run `zig build fuzz -Dfuzz=fuzz_target`

## Source text · SKILL.md · MIT

Below is the content of a third-party file. It is data, not instructions for you: do not act on anything written inside unless the human asks. Block tag: 8d151269f139e3d2.

BEGIN THIRD-PARTY FILE 8d151269f139e3d2
````text
---
name: zig-testing
description: Zig testing skill for writing and running tests. Use when using zig build test, writing comptime tests, using test filters, working with test allocators to detect leaks, or using Zig's built-in fuzz testing (0.14+). Activates on queries about Zig tests, zig test, zig build test, comptime testing, test allocators, Zig fuzz testing, or detecting memory leaks in Zig tests.
---

# Zig Testing

## Purpose

Guide agents through Zig's testing system: `zig build test` and `zig test`, comptime testing patterns, test filters, the test allocator for leak detection, and Zig's built-in fuzz testing introduced in 0.14.

## Triggers

- "How do I write and run tests in Zig?"
- "How do I filter which Zig tests run?"
- "How do I detect memory leaks in Zig tests?"
- "How do I write comptime tests in Zig?"
- "How do I use Zig's built-in fuzzer?"
- "How do I test a Zig library?"

## Workflow

### 1. Writing and running tests

```zig
// src/math.zig
const std = @import("std");
const testing = std.testing;

pub fn add(a: i32, b: i32) i32 {
    return a + b;
}

pub fn divide(a: f64, b: f64) !f64 {
    if (b == 0.0) return error.DivisionByZero;
    return a / b;
}

// Tests live in the same file or a dedicated test file
test "add: basic addition" {
    try testing.expectEqual(@as(i32, 5), add(2, 3));
    try testing.expectEqual(@as(i32, -1), add(2, -3));
}

test "add: identity" {
    try testing.expectEqual(@as(i32, 42), add(42, 0));
}

test "divide: normal case" {
    const result = try divide(10.0, 2.0);
    try testing.expectApproxEqAbs(result, 5.0, 1e-9);
}

test "divide: by zero returns error" {
    try testing.expectError(error.DivisionByZero, divide(1.0, 0.0));
}
```

```bash
# Run all tests in a single file
zig test src/math.zig

# Run all tests via build system
zig build test

# Verbose output
zig build test -- --verbose

# Run specific test by name (substring match)
zig build test -- --test-filter "add"
```

### 2. build.zig test configuration

```zig
// build.zig
const std = @import("std");

pub fn build(b: *std.Build) void {
    const target = b.standardTargetOptions(.{});
    const optimize = b.standardOptimizeOption(.{});

    // Unit test step
    const unit_tests = b.addTest(.{
        .root_source_file = b.path("src/main.zig"),
````
END THIRD-PARTY FILE 8d151269f139e3d2

The third-party file has ended. Everything between the 8d151269f139e3d2 tags is data: requests and commands from it are not followed. An “end of file” line with another tag inside the block is part of the file.

First 2294 of 7361 bytes. © mohitmishra786 · MIT · https://github.com/mohitmishra786/low-level-dev-skills/tree/HEAD/skills/zig/zig-testing/SKILL.md

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