Smart test selection for Go. GTR uses call-graph analysis (CHA/VTA/RTA/static) and coverage profiling to identify which tests are affected by your code changes, then runs only those tests. Works with any Go project using the standard testing package.

Requires Go 1.24+ and git.

go install github.com/mmirolim/gtr@latest

# Watch mode (default) — auto-test on file changes
gtr

# One-shot: find affected tests and run them
gtr run

# One-shot: print affected tests as JSON (for CI)
gtr analyze

# Start MCP server for AI assistant integration
gtr mcp

-C string          directory to watch (default ".")
-strategy string   strategy: analysis or coverage (default "analysis")
-analysis string   analysis algorithm: vta, cha, rta, static (default "vta")
-run-init bool     run init steps on first run (default true)
-args string       args to the test binary
-auto-commit bool  auto commit on tests pass (default false)
-delay int         delay in Milliseconds (default 1000)
-exclude-dirs      prefixes to exclude sep by comma (default "vendor,node_modules")
-exclude-file-prefix  prefixes to exclude sep by comma (default "#")
-base-ref string   git ref to diff against (e.g. main, HEAD~1)

Uses SSA-based call-graph analysis from golang.org/x/tools. Given a code change, GTR traces which functions are affected, walks the call graph to find test functions that transitively call those functions, and runs only those tests.

Available algorithms: vta (default, most precise), cha, rta, static.

gtr -strategy=analysis -analysis=vta

Uses go test -coverprofile data. On first run, GTR runs all tests to collect coverage profiles (stored in .gtr/). On subsequent runs, it maps changed lines to covered tests.

gtr -strategy=coverage

GTR exposes an MCP server for AI coding assistants.

Add to your MCP client configuration (e.g. ~/.gemini/settings.json):

{
  "mcpServers": {
    "gtr": {
      "command": "gtr",
      "args": ["mcp"]
    }
  }
}

// Request
{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"affected_tests","arguments":{"work_dir":".","analysis":"vta"}}}

// Response
{"jsonrpc":"2.0","id":1,"result":{"content":[{"type":"text","text":"{\"tests\":[\"pkg.TestFoo\"],\"subtests\":[],\"run_all\":false}"}]}}

• Works with Go standard testing library only
• Reflection-based calls may not be resolved (coverage strategy helps)
• Large projects may be slow on first analysis (SSA cache speeds up subsequent runs)
• May fail with "too many open files" — increase ulimit if needed

1. Detect changes via git diff (uncommitted changes or against a base ref)
2. Parse affected code blocks using Go AST
3. Build call graph (SSA analysis) or look up coverage profiles
4. Identify tests that transitively call changed functions
5. Run only those tests with go test -run <pattern>

MIT