docs(go): add core test command documentation

Documents the new `core test` command with:
- All flags and options
- Example usage patterns
- Output samples (default, coverage, JSON)
- macOS linker warning suppression feature
- Coverage colour coding explanation

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/packages/go/cmd/test.md

@@ -0,0 +1,134 @@
+# core test
+
+Run Go tests with coverage reporting and clean output.
+
+## Usage
+
+```bash
+core test [flags]
+```
+
+## Flags
+
+| Flag | Description |
+|------|-------------|
+| `--verbose` | Stream test output as it runs |
+| `--coverage` | Show detailed per-package coverage breakdown |
+| `--pkg <pattern>` | Package pattern to test (default: `./...`) |
+| `--run <regex>` | Run only tests matching this regex |
+| `--short` | Skip long-running tests |
+| `--race` | Enable race detector |
+| `--json` | Output JSON for CI/agents |
+
+## Examples
+
+```bash
+# Run all tests with coverage summary
+core test
+
+# Show test output as it runs
+core test --verbose
+
+# Show detailed coverage by package
+core test --coverage
+
+# Test specific packages
+core test --pkg ./pkg/crypt
+core test --pkg ./pkg/...
+
+# Run specific tests by name
+core test --run TestHash
+core test --run "Test.*Good"
+
+# Skip integration tests
+core test --short
+
+# Check for race conditions
+core test --race
+
+# CI/agent mode with JSON output
+core test --json
+```
+
+## Output
+
+### Default Output
+
+```
+Test: Running tests
+  Package: ./...
+
+  ✓ 14 passed
+
+  Coverage: 75.1%
+
+PASS All tests passed
+```
+
+### With `--coverage` Flag
+
+```
+Test: Running tests
+  Package: ./...
+
+  ✓ 14 passed
+
+  Coverage by package:
+    pkg/crypt              91.2%
+    pkg/crypt/lthn         100.0%
+    pkg/io                 96.0%
+    pkg/plugin             93.3%
+    pkg/runtime            83.3%
+    pkg/workspace          73.9%
+    pkg/container          65.6%
+    pkg/release            40.8%
+    pkg/php                26.0%
+    pkg/release/publishers 13.3%
+
+    Average                75.1%
+
+PASS All tests passed
+```
+
+### JSON Output (`--json`)
+
+```json
+{
+  "passed": 14,
+  "failed": 0,
+  "skipped": 0,
+  "coverage": 75.1,
+  "exit_code": 0,
+  "failed_packages": []
+}
+```
+
+## Features
+
+### macOS Linker Warning Suppression
+
+Sets `MACOSX_DEPLOYMENT_TARGET=26.0` automatically to suppress CGO linker warnings on macOS. The warnings are also filtered from output for clean DX.
+
+### Coverage Colour Coding
+
+Coverage percentages are colour-coded:
+- **Green**: 80%+ coverage
+- **Amber**: 50-79% coverage
+- **Red**: Below 50% coverage
+
+### Package Name Shortening
+
+Package names are shortened for readability:
+- `github.com/host-uk/core/pkg/crypt` → `pkg/crypt`
+
+## Exit Codes
+
+| Code | Meaning |
+|------|---------|
+| 0 | All tests passed |
+| 1 | One or more tests failed |
+
+## See Also
+
+- [build command](build.md) - Build Go projects
+- [doctor command](doctor.md) - Check development environment

docs/packages/go/index.md

@@ -39,6 +39,7 @@ curl -fsSL https://github.com/host-uk/core/releases/latest/download/core-$(uname
 |---------|-------------|
 | [`core dev`](cmd/dev.md) | Portable development environment (100+ tools) |
 | [`core php`](cmd/php.md) | Laravel/PHP development tools |
+| [`core test`](cmd/test.md) | Run tests with coverage reporting |
 | [`core doctor`](cmd/doctor.md) | Check development environment |
 
 ### GitHub & Multi-Repo
@@ -104,6 +105,7 @@ Core uses `.core/` directory for project configuration:
 - [Templates](cmd/templates.md) - LinuxKit templates
 - [Dev](cmd/dev.md) - Portable development environment
 - [PHP](cmd/php.md) - Laravel development
+- [Test](cmd/test.md) - Run tests with coverage
 - [Doctor](cmd/doctor.md) - Environment check
 - [Search & Install](cmd/search.md) - GitHub integration
 - [Setup](cmd/setup.md) - Clone repos from registry