Function testsForShard

cmd/testwrapper/testwrapper.go:176–230

testsForShard returns the test names in pkg that belong to the given shard spec (e.g. "2/3"). It uses "go list -json" to find test source files (no compilation) and scans them for top-level test function names, assigning each to a shard by hashing. Returns nil if the spec is invalid or if listing fa

(ctx context.Context, pkg, shardSpec string)

// each to a shard by hashing. Returns nil if the spec is invalid or if
// listing fails (the main run will surface the error).
func testsForShard(ctx context.Context, pkg, shardSpec string) ([]string, error) {
	a, b, ok := strings.Cut(shardSpec, "/")
	if !ok {
		return nil, nil
	}
	wantShard, err := strconv.Atoi(a)
	if err != nil || wantShard < 1 {
		return nil, nil
	}
	shards, err := strconv.Atoi(b)
	if err != nil || shards < 1 {
		return nil, nil
	}

	out, err := exec.CommandContext(ctx, "go", "list", "-json", pkg).Output()
	if err != nil {
		// Errors will be surfaced by the main test run.
		return nil, nil
	}

	type pkgJSON struct {
		Dir          string
		TestGoFiles  []string
		XTestGoFiles []string
	}

	seen := map[string]bool{}
	var result []string

	dec := json.NewDecoder(bytes.NewReader(out))
	for dec.More() {
		var p pkgJSON
		if err := dec.Decode(&p); err != nil {
			break
		}
		for _, f := range append(p.TestGoFiles, p.XTestGoFiles...) {
			names, err := testFuncNames(filepath.Join(p.Dir, f))
			if err != nil {
				continue
			}
			for _, name := range names {
				if seen[name] {
					continue
				}
				seen[name] = true
				h := fnv.New32a()
				io.WriteString(h, name)
				if int(h.Sum32()%uint32(shards)) == wantShard-1 {
					result = append(result, name)
				}
			}
		}
	}
	return result, nil
}

// testFuncNames scans a Go source file and returns the names of all top-level
// test functions (Test*, Benchmark*, Example*, Fuzz*).